The study investigated teachers' competency in using technological and pedagogical content knowledge in teaching scientific concepts in Senior Secondary Schools in Ondo State, Nigeria. The study adopted non-experimental design involving descriptive research of the survey type. The population was made up of all science teachers and principals in public secondary schools in Ondo State. The sample consisted of 628 science teachers and 132 principals. Multi-stage sampling procedure was used to select 132 secondary schools in 12 local government areas across the three senatorial districts of Ondo State. The instruments used for the study were Technological and Pedagogical Content Knowledge Questionnaire (TPCKQ) with coefficient r = (0.93) and Teachers' Professional Competency Questionnaire (TPCQ) with coefficient r = (0.84). Research questions were answered using descriptive statistics. Six research hypotheses were generated and tested by employing inferential statistics at 0.05 levelof significance.