diff --git a/src/Utils.php b/src/Utils.php
index 73536f1..0cbf3d4 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -62,6 +62,14 @@ class Utils
         'tether' => '1000000000000000000000000000000'
     ];
 
+    /**
+     * NEGATIVE1
+     * Cannot work, see: http://php.net/manual/en/language.constants.syntax.php
+     * 
+     * @const
+     */
+    // const NEGATIVE1 = new BigNumber(-1);
+
     /**
      * construct
      *
@@ -126,7 +134,7 @@ class Utils
     public static function isZeroPrefixed($value)
     {
         if (!is_string($value)) {
-            throw new InvalidArgumentException('The value to zeroPrefixed function must be string.');
+            throw new InvalidArgumentException('The value to isZeroPrefixed function must be string.');
         }
         return (strpos($value, '0x') === 0);
     }
@@ -146,6 +154,20 @@ class Utils
         return $value;
     }
 
+    /**
+     * isNegative
+     * 
+     * @param string
+     * @return bool
+     */
+    public static function isNegative($value)
+    {
+        if (!is_string($value)) {
+            throw new InvalidArgumentException('The value to isNegative function must be string.');
+        }
+        return (strpos($value, '-') === 0);
+    }
+
     /**
      * isAddress
      * 
@@ -415,25 +437,44 @@ class Utils
      * Change number or number string to bignumber.
      * 
      * @param BigNumber|string|int $number
-     * @return \phpseclib\Math\BigInteger
+     * @return array|\phpseclib\Math\BigInteger
      */
     public static function toBn($number)
     {
-        if (is_numeric($number)) {
+        if ($number instanceof BigNumber){
+            $bn = $number;
+        } elseif (is_int($number)) {
             $bn = new BigNumber($number);
+        } elseif (is_numeric($number)) {
+            $number = (string) $number;
+
+            if (self::isNegative($number)) {
+                $count = 1;
+                $number = str_replace('-', '', $number, $count);
+                $negative1 = new BigNumber(-1);
+            }
+            $bn = new BigNumber($number);
+
+            if (isset($negative1)) {
+                $bn = $bn->multiply($negative1);
+            }
         } elseif (is_string($number)) {
             $number = mb_strtolower($number);
 
+            if (self::isNegative($number)) {
+                $count = 1;
+                $number = str_replace('-', '', $number, $count);
+                $negative1 = new BigNumber(-1);
+            }
             if (self::isZeroPrefixed($number) || preg_match('/[a-f]+/', $number) === 1) {
                 $number = self::stripZero($number);
                 $bn = new BigNumber($number, 16);
-            } else {
-                $bn = new BigNumber($number);
             }
-        } elseif ($number instanceof BigNumber){
-            $bn = $number;
+            if (isset($negative1)) {
+                $bn = $bn->multiply($negative1);
+            }
         } else {
-            throw new InvalidArgumentException('toBn number must be BigNumber, string or int.');
+            throw new InvalidArgumentException('toBn number must be BigNumber, numeric string or int.');
         }
         return $bn;
     }
diff --git a/test/unit/UtilsTest.php b/test/unit/UtilsTest.php
index 96e3ddd..7673e5d 100644
--- a/test/unit/UtilsTest.php
+++ b/test/unit/UtilsTest.php
@@ -448,6 +448,20 @@ class UtilsTest extends TestCase
         $this->assertFalse($isHex);
     }
 
+    /**
+     * testIsNegative
+     * 
+     * @return void
+     */
+    public function testIsNegative()
+    {
+        $isNegative = Utils::isNegative('-1');
+        $this->assertTrue($isNegative);
+
+        $isNegative = Utils::isNegative('1');
+        $this->assertFalse($isNegative);
+    }
+
     /**
      * testToBn
      * 
@@ -461,12 +475,27 @@ class UtilsTest extends TestCase
         $bn = Utils::toBn('0x12');
         $this->assertEquals($bn->toString(), '18');
 
+        $bn = Utils::toBn('-0x12');
+        $this->assertEquals($bn->toString(), '-18');
+
         $bn = Utils::toBn(0x12);
         $this->assertEquals($bn->toString(), '18');
 
         $bn = Utils::toBn('ae');
         $this->assertEquals($bn->toString(), '174');
 
+        $bn = Utils::toBn('-ae');
+        $this->assertEquals($bn->toString(), '-174');
+
+        $bn = Utils::toBn('-1');
+        $this->assertEquals($bn->toString(), '-1');
+
+        // $bn = Utils::toBn('-0.1');
+        // $this->assertEquals($bn->toString(), '-0.1');
+
+        // $bn = Utils::toBn(-0.1);
+        // $this->assertEquals($bn->toString(), -0.1);
+
         $bn = Utils::toBn(new BigNumber(1));
         $this->assertEquals($bn->toString(), '1');