The study investigated creativity, academic motivation and achievement belief as determinants of mental ability of senior secondary school students in Mathematics in Anambra state, Nigeria. Four research questions guided the study and four hypotheses were tested at 0.05 level of significance. The predictive correlation design was adopted for the study. The population of the study comprised 21,204 senior secondary two SS2 students in Anambra State, out of which 720 students obtained using random and purposive sampling techniques were involved in the study. The instruments for data collection were validated by three experts from the Departments of Science Education and Educational Foundations (Measurement and Evaluation), Nnamdi Azikiwe University, Awka. The reliability of creativity inventory, academic motivation scale and achievement beliefs scale was established using Cronbach Alpha while that of Mental Ability Test (MAT) was established using KR-20 which yielded coefficient value of .72 for Creativity inventory, .73 for academic motivation scale, .71 for achievement beliefs scale and .73 for Mental Ability Test. Creativity inventory, academic motivation scale, achievement beliefs scale and mental ability test were administered on the students with the help of six research assistants. Data obtained were analyzed using simple and multiple linear regressions. The findings of the study among others revealed that creativity, academic motivation, and achievement beliefs jointly made significant contribution to the prediction of students’ mental ability. Among the predictors, academic motivation showed the highest beta weight, indicating that motivated students tend to exhibit higher mental ability in Mathematics. Creativity also positively influenced mental ability in Mathematics, while achievement beliefs enhanced students’ mental ability in Mathematics. Based on the above findings. It was recommended among others that teachers and school administrators design instructional strategies that foster creativity, sustain academic motivation and strengthen positive achievement beliefs to improve students’ mental ability.