Objective: The aim of this study is the calculation of measurement uncertainty values of ten different iochemical parameters by using internal and external quality control datas with three different, but same model and trademark device and the comparison of these values with Fraser’s and CLIA’s total allowable error % (TEa%) values. Methods: In the calculation of measurement uncertainty, six step “uncertainty calculation model”, that is defined in Nordest guide which is based on European Accreditation Guideline/12 /, European Technical Report: 1/3/and ISO/DTS 21748 Guideline/8/was used. Results: TEa% values of blood urea nitrogen for Device A, potassium values for Device B and albumin, creatinine, sodium and total protein values for Device C were found to be higher when compared to TEa% values of Fraser. TEa% of blood urea nitrogen, which has been calculated for Device A, B and C was found to be higher when compared to TEa% values of CLIA. TEa% values which has been calculated for glucose, AST, cholesterol and triglyceride in each three device was not found to be higher than TEa% values of CLIA and Fraser. Conclusion: Laboratories should establish the model for calculation of uncertainity measurement and evaluation criterias and take the analytical difference between devices under control. Also they should give the results which are not exceeding the targeted TEa% values and should inform the clinicians about it.