Depending on the effect of technology on organizations and work, a remarkable factor for solving human-oriented problems is having an employee congruent with his/her group. Considering fit as a tool for creating this employee profile has become a research topic in the field of human resource management for the last several years. One of the effects related to fit/misfit is group performance. The effect of employees’ fit with their group on the performance of working group is investigated in this research. Person-group fit is investigated by means of 3 dimensions: the employees’ perception about demographic similarity with group members (relational demography, similarity of personal values with group values, and congruence of personality traits with group members’ ones. 124 working group-sampling is selected at technology based organizations. The volume of selected sampling is 640 employees. Proposed relationships are tested by means of structural equation modelling at lisrel program. According to findings, employees’ perception of demographic similarity concerning group and value fit affect group performance, positively as expected. Contrary to expectations, personality traits similarity with group members explain the variance in the group performance, negatively.