This paper is concerned with how the implementation of Mobile Number portability in Nigeria (MNP) has affected the revenue of mobile operators in Nigeria. It gives an overview of marked effect of MNP on revenue of mobile operators in Nigeria by comparing statistics, rate of porting and taking case studies. When MNP was launched on the 22^nd of April 2013 by the Nigerian Communications Commission (NCC) it seemed to be received well by operators. Over a space of 3 years since it was launched some operators have gained customers and some have lost customers through MNP. This gain and loss of customers has had a direct effect on the revenue of these operators making some operators to place higher than they had before in terms of revenue and others to place lower in terms of revenue. Competition between mobile operators to get customers has increased greatly as more customers mean more money and this goes to show that MNP has had a significant impact on the revenue of mobile operators.