Background and Objective: Quality control is one of the most important components in order to improve quality assurance in laboratories during analytical steps. For this purpose, coefficient of variation plays an important role. Due to the fast improvement in technology, application of inferential statistics for the comparisons of laboratory techniques, including instrument and chemicals and fast replacement of them would be technically essential. Materials and Methods: In this research study, we tried to determine the precision of one auto-analyzer with refrigerator and the other one without such facility for the analysis of glucose, triglyceride and cholesterol in 30 successive days and compared the coefficient of variations that are an important factor for analytical precision. Results: Comparing the means of aimed groups by paired t-test with P=0.05 in measurement of glucose, triglyceride and cholesterol showed that there was no significant difference between the two instruments. In determination of glucose, triglyceride and cholesterol by auto-analyzer with refrigerator, CV% of these analytes was 1.3%, 1.4%, and 0.9% respectively. By the auto-analyzer without refrigerator, the CV% of those analytes was 1.5%, 2.5% and 1.11% respectively. Conclusion: There is reasonably higher precision for auto-analyzer with refrigerator than the other one.