Given oracle access to a Boolean function f:01n01 , we design a randomized tester that takes as input a parameter 0">\eps0, and outputs {\sf Yes} if the function is monotone, and outputs {\sf No} with probability 2/3">23 , if the function is \eps-far from monotone. That is, f needs to be modified at \eps-fraction of the points to make it monotone. Our non-adaptive, one-sided tester makes O(n78\eps−32) queries to the oracle.