Background and Objective: Early detection of ectopic pregnancy is crucial in saving fertility. Some chemical biomarkers that can differentiate normal intra uterine pregnancy from ectopic pregnancy have been detected. This study was performed to determine the sensitivity and specificity of serum creatine phosphokinase(CPK) measurement for diagnosis of ectopic pregnancy. Materials and Methods: This study was performed in Kosar Hospital, Qazvin University of Medical Sciences. Twenty six patients with confirmed ectopic pregnancy comprised the study group and 29 cases with normal intrauterine pregnancy less than 12 weeks constituted the control group. The study group was further subdivided into two groups of ruptured and unruptured tubal pregnancy. A blood sample was obtained from each patient on admission and then CPK was measured. The collected data were analyzed using t-test and k2. Then, CPK levels were compared in three groups. Results: The mean CPK levels in the study group (156+ 93.6 IU/ml) were significantly higher than the control group (58.6+31.5 IU/ml) (P =0.0001). Also the mean CPK levels were higher in ruptured (220.8+100.5 IU/ml) than in unruptured cases (104.3+21.4 IU/ml) (P =0.002). Sensitivity, specificity, positive predictive value, and negative predictive values of CPK in diagnosis of tubal pregnancy were 92%, 86%, 85.7%, and 92.5%, respectively. Conclusion: Serum CPK is considered as a valuable measurement for diagnosis of tubal pregnancy. It is also a useful biomarker in discriminating ruptured from unruptured cases.