This study verified the differential item functioning of secondary school student’s achievement in mathematics. One research question and one null hypothesis guided the study. The SS2 students in Abi Local Government Area. Secondary Schools for 2018/2020 session constituted the population. A sample of 70 students selected through stratified sampling technique was used for the study. A 25 items standardized instrument captioned mathematics Achievement Test (MAT) based on SS II mathematics curriculum was used. The research questions was answered using 1RT statistic called DIF contrast, while the hypothesis were tested at .05 levels of significance using Student t-test statistics. All these statistics were generated by the IRT software WINSTEPS 3.92.1. The results of the analysis indicated that male and female examinees function differential in 15 items and no difference in 10 items. The results also revealed that four out of the twenty-five items were significantly biased against gender. On the basis of the analysis, it becomes necessary that the examining bodies should set and administer items that are fair to enhance appropriate interpretation of students’ results