Objective: The measurement of compounded topical medications’ uniformity is an important component of quality assessment. This study was aimed to evaluate appropriate mixing time for external preparations using a planetary centrifugal mixer.Methods: In order to evaluate the product uniformity of mixtures of five different steroid cream (Antebate®, Myser®, Methaderm®, Lidomex®, and Locoid®) with three different heparinoid oil-based cream (Hirudoid®, “Nichi-Iko” cream and “Nipro” cream), steroid cream and heparinoid oil-based cream (5 g each) were added into a 13 mL container and mixed using the mixer (NanKo Rentaro NRE-120®, THINKY) at rotation speed of 800 rpm and revolution speed of 2,000 rpm. We sampled 0.1 g of the mixture from three spots (top, middle, and bottom portions) of the container then, measured the steroid content by HPLC method. The yield value points of each cream and heparinoid oil-based cream were also measured by spread meter.Results: Our results showed that when the coefficient of variation (CV) is less than 15.2 %, a mixing time of at least 120 s was required to achieve proper mixing to obtain the permissible limit of steroid cream and heparinoid oil-based cream. Also the greater difference of the yield value between steroid cream and heparinoid oil-based cream tended to be mixed easier.Conclusions: These results suggest that the spread ability of steroid cream and heparinoid oil-based cream affects the mixing efficiency of a planetary centrifugal mixer.