By this research, it is aimed to determine the effect of in-service training was designed due to Rieber and Welliver's (1989) technology integration model to the secondary school mathematics teachers' technology usage level. The in-service course was conducted over a 15-week period and 13 secondary school mathematics teachers from Bayburt participated in the course. When the course program was being structured, some software and learning objects developed for mathematics teaching were utilized. The applications were supported by worksheets and activity examples appropriate for the curriculum. In this study where data were gathered using interviews and observations, the case study method was used. The collected data was analysed by means of qualitative and quantitative analysis methods. When the findings were checked, it can be seen a result that teachers took advantage of technology for composing deep conceptual comprehension and structuring concepts by students centred explores and used technology in their lessons frequently. By this manner, it was resulted that the designed course positively affected to teacher's technology usage levels.