This study assessed unidimensionality and occurrence of Differential Item Functioning (DIF) in Mathematics and English Language items of Osun State Qualifying Examination. The study made use of secondary data. The results showed that OSQ Mathematics (-0.094 = r = 0.236) and English Language items (-0.095 = r = 0.228) were unidimensional. Also, there was occurrence of DIF items in both Mathematics and English Language multiple-choice items of the OSQE for 2008. Fourteen items representing 28% of the 50 items in the Mathematics examination exhibited DIF and 10 items, representing 20% of the 50 items in the English Language examination exhibited DIF. The study concluded that the Examination contained considerable number of items that exhibited DIF and therefore requires adequate item quality improvement to justify its use as the inclusion or exclusion criterion of state candidate in West African Examination Council.