The present study aimed to develop science teaching competence belief scale (STCBS). Secondly, the study also investigated whether science teachers (STs) and pre-service science teachers' (PSTs) competence beliefs regarding science teaching in the resource room differed with respect to certain variables. Another purpose was to determine the predictive effect of gender, education level, legislation knowledge, self-confidence, affective tendencies and knowledge and skills related to some key concepts on STs and PSTs' science teaching competence belief (STCB) scores. Quantitative research methods were used in this study. The research data were collected from 336 STs and PSTs for the validity and reliability of the STCBS. According to the exploratory factor analysis results conducted after item analysis, the scale consisted of 35 items with five sub-dimensions. The Cronbach's alpha reliability coefficient of the overall scale was found to be 0.92. The STCBS was applied to 287 STs and PSTs to determine whether there was a predictive effect of certain variables on STs and PSTs' STCB scores. The results of the study revealed significant differences in favour of fourth-grade PSTs and in favour of PSTs who took special education lessons. As a result, it was found that there was a negative relationship between STs' workload and STCB scores. Also, there was a positive relationship between professional experience and STs' responsibilities to teach science to special education students. The study also revealed that collaboration with special education teachers, parents and school administration increased STs' STCB scores. In addition, there was no relationship between the resource room experiences of STs and STCB scores. The results of the study demonstrated that gender, self-confidence, affective tendencies and knowledge and skills related to mainstreaming/inclusion and evaluation from key concepts were significant predictors of STCB.