This project seeks to examine the relationship between cohesion and collective efficacy in Tunisian sport's team. A total of 463 athletes (313 males, M age= 17,3, SD = 2.09 and 150 females, M age = 19.15, SD = 3.32) were recruited from 18 Tunisian amateur sport team. This sample complete the Tunisian version of GAG (group environment questionnaire, Heuzé et Fontayne, 2002) and a collective efficacy measure validate for this study which is the second objective of this research: the validity of a Tunisian (classical Arabic) translation of the Collective Efficacy Questionnaire in Sports (CEQS). Confirmatory factor, internal consistency and correlation analysis among subscales were performed. The statistical analyses undertaken provide the psychometric character of the Tunisian CEQS (α = 0.92).This study also revealed a positive and significantly relationship between the dimensions of cohesion and collective efficacy. However, subsequent multiple regression analyses indicated that collective efficacy is more related to task cohesion than social cohesion. More than, Tunisian Players who perceived a higher level of task cohesion also tended to report higher collective efficacy judgments.