Aims:The paper empirically investigated the effect of mandatory adoption of International Financial Reporting Standards on earnings predictability of deposit money banks and insurance firms. Study Design: It adopted ex post facto research design. Place and Duration of Study:The study was conducted in Nigeria and covered the period 2008 to 2014. Methodology: The study used 196 firm-year observations obtained from annual reports of the deposit money banks and insurance firms quoted on the Nigerian Stock Exchange. It formulated two hypotheses and tested the hypotheses using random effect model of Generalized Least Square Method. Results: The regression results revealed that the mandatory adoption of IFRS did not improve earnings predictability of firms in the services sector, based on earnings and cash flows. The results Ebirien et al.; JEMT, 24(1): 1-12, 2019; Article no.JEMT.49287 2 also showed that the earnings predictability in the post mandatory IFRS adoption period was not significantly different between DMBs and insurance firms. Conclusions: Nigeria has relatively short IFRS experience and preparers are still contending with several evolving issues. The paper recommends sustained training for both the preparers, users and regulators so as to improve financial reporting and consequently enhance earnings predictability. Original Research Article