Oscillating heat pipe (OHP) has been widely studied as a promising heat transfer device. In the current investigation, the effect of working fluid, filling ratio, operating temperature and orientation on the operating limit was investigated. Water and HFE-7100 was charged into the OHP, respectively. The result shows that (1) the operating limit depends on the working fluid significantly; (2) the operating limit increases as the filling ratio increases; (3) the operating limit increases as the tilt angle increases; (4) the operating limit increases as the operating temperature increases when the OHP is charged with HFE-7100; (5) however, the operating limit decreases as the temperature increases when the OHP is charged with water. Finally, a semi-empirical model predicting the operating limit of the OHP was developed and verified based on test results. Comparing the test results, the relative error of operating limit predicted by the model is less than 30%.