The concept of collective efficacy that can be defined as "a belief in their common ability to organize and realize plans to achieve goals" (Bandura, 1997, p. 477) has gained utmost importance in educational contexts. Therefore, there arises an emergent need to develop scales to evaluate teachers' collective efficacy behaviours. To this end, the present study aimed to develop an instrument to assess collective teacher efficacy behaviours. For this purpose in mind, an item pool was created in line with the related literature and face-to-face interviews with teachers. Two participating groups were included in the study. There was a total of 833 participants, 475 of which were in the first group and 358 in the second group.The preliminary version of The Collective Teacher Efficacy Behaviours Scale (CTEBS), consisted of 26 items. Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) were employed to test the construct validity of the scale with the available datasets. As a result of the EFA, a two-factored structure, namely social and professional relationship and professional development, was identified with 20 items. The two factors explained 58.798% of the total variance. Confirmatory factor analysis (CFA) was used to test the validity of the structure based on the EFA results. It was found that the CFA fit indices were X[superscript 2]/df=3.174, RMSEA=0.076, SRMR=0.435, NFI=0.902, CFI=0.930, IFI=0.931, and GFI=0.872. The results implied that The Collective Teacher Efficacy Behaviours Scale, consisting of two dimensions and 20 items, was a valid and reliable instrument.