To examine the microscale filling imbalance in the present work, an eight-cavity injecting mold with microcylindrical-hole arrays fabricated by micro-electrical discharge machining milling technology was developed. Polypropylene (PP) was used to carry out single factor filling flow experiments with vacuuming the mold cavities. The filling height difference of micro cylindrical hole at the same position between cavity I and cavity II, which was the index of filling imbalance and the effect of mold temperature and injection rate on the filling imbalance of microholes with diameters of 200 mu m and 300 mu m was investigated. The results revealed that the maximum height difference reached 101 mu m with low process parameters, and the filling imbalance was obvious. With the increase in mold temperature and injection rate, the filling imbalance was weakened. In addition, the impact of the scale effect on filling imbalance was checked. The filling imbalance of micro holes in 200 mu m was greater than that in 300 mu m using identical process parameters. With the increase in mold temperature and injection rate, the filling height difference of the two kinds of micro holes decreased. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers