This study examined teachers’ professional competencies as determinants of students’ academic achievement in Mathematics in Uyo Education Zone of Akwa Ibom State, Nigeria. Two hypotheses were formulated to guide the study. Literature relating to the variables under study was reviewed. Ex-post facto research design was adopted. A sample of 800 out of 7479 students was selected using stratified and simple random sampling procedure. The instruments titled Teachers’ Professional Competencies (TPC) and Mathematics Academic Achievement Test (MAAT) Items were used for data collection. The reliability estimate of the TPC was established using Cronbach Alpha giving a reliability estimate of .78 for teachers’ lesson presentation and .79 for teachers’ knowledge of the subject mastery while MAAT was established using Kuder Richardson formula K-R20 at. 80. These estimates having met the criterion for stability, warranted in use for data collection. Linear Regression was adopted to test the two hypotheses at .05 level of significance. The result of the analysis revealed that teachers’ lesson presentation and teachers’ knowledge of subject mastery significantly predicts students’ academic achievement in Mathematics. Based on this finding, it was recommended among others that teachers should regularly attend conferences, seminars and workshops of stakeholders in education in order to improve their competence in lesson presentation, subject mastery and enhance students’ academic achievement in Mathematics.