This study presents the impacts of suitable refrigerant charge to test the performance of laboratory refrigerator rig for using three refrigerants of (R134a, R600a and R290) instead of R12 .The coefficient of performance and maximum consumption amperes are taken as function to evaluate the optimum charge of these refrigerants. The results imply that the over refrigerant charge will reduce the system performance. Compared the optimum refrigerant charge of R600a is (45g), R290 is (70 g) and R134a is (60g), instead of R12. The results show that the refrigerator with R134a gives lowest capacity reduction with same performance to R12 from other alternative refrigerant, and can be taken as the best alternative refrigerant.