Abstract Since about 100 years, social loafing has been studied as one of the most important factors lowering working group efficiency in organizations. Considering many employees activities are related to each other and has done in group context now days, in this research we are going to identify factors affecting social loafing in private sector employees. Our case was FANAP employees in Telecom project. This research approach is qualitative and uses analytical methods, and from data collection aspect it is survey and applied from conclusions aspect. At the framework of this survey, cognitive mapping method is used to map individual perceptions about causes of social loafing. Analyzing methods of cognitive maps is used for complexity indexes, Domain analyses, central analyses, consequence analyses and analyses of consensus cognitive maps. Finally conclusions are grouped in four levels as personal factors, group factors, organization factors and job factors that affecting social loafing. Factors such as extrinsic motivation, job dissatisfaction, intrinsic motivation, perception lack of group cohesion were agreed more than other factors in perception of the participants of this research.