diff --git a/allalgorithms/numeric/countOnes.py b/allalgorithms/numeric/countOnes.py
new file mode 100644
index 0000000..c184c0a
--- /dev/null
+++ b/allalgorithms/numeric/countOnes.py
@@ -0,0 +1,25 @@
+# -*- coding: UTF-8 -*-
+#
+# count ones in a array
+# The All ▲lgorithms library for python
+#
+# Contributed by: Natan Lucena
+# Github: @NatanLucena
+#
+
+
+def countOnes(arr,low,high): 
+      
+    if high>=low: 
+           
+        mid = low + (high-low)/2
+           
+        if ((mid == high or arr[mid+1]==0) and (arr[mid]==1)): 
+            return mid+1
+ 
+        if arr[mid]==1: 
+            return countOnes(arr, (mid+1), high) 
+
+        return countOnes(arr, low, mid-1) 
+      
+    return 0