Microinjection molding has been drawing more and more attention due to its great advantages such as cost effectiveness and mass production capability. In this work, an experimental study was carried out in order to investigate the effect of the mold surface roughness on the achieved filled length of the molded microfeatures. For this purpose, an aluminum mold insert with microchannels having different surface roughness values was designed and fabricated using ultraprecision diamond machining and micromilling method. The experimental results revealed that increasing surface roughness of the microchannel wall led to a decrease in the filled length of the molded microfeatures. It was also found that with increased melt temperature or injection velocity, the effect of surface roughness was weakened by high-pressure trapped air inside the microchannels during injection process. Finally, the influence mechanism of the mold surface roughness was discussed.