The aim of this study was to examine the pre-service mathematics teachers' technological pedagogical content knowledge and beliefs using computer technology in mathematics instruction, as well as the effects of teacher training programs on these beliefs and knowledge. Participants included 199 pre-service elementary mathematics teachers. Of these, one hundred-eighteen were freshman and eighty-one were senior. Two instruments (Technological Pedagogical Content Knowledge (TPACK) instrument and Belief Scale towards Using Computer Technology in Mathematics Instruction) were used to determine pre-service teachers' TPACK and beliefs about using computer technology in their instruction. To evaluate pre-service teachers' TPACK and beliefs, both descriptive and inferential statistics were used. The data showed that the teacher education program has a positive effect on pre-service teachers' TPACK for mathematics teaching and beliefs using computer technology in mathematics instruction. In addition, there was a positive correlation between pre-service teachers' belief scores and TPACK scores. So, it can be said that the beliefs using computer technology into instruction is a significant predictor for TPACK.