This study photo-etches micropatterns on mold inserts and manufactures a light guide plate with microstructures using microinjection molding. The single parameter method is used to investigate flatness and replication with different process parameters for microinjection molding. Mold temperature is the most important factor for plate flatness and microstructure replication of a light guide plate fabricated by microinjection molding. Low mold temperature increases the flatness of light guide plates, whereas a high mold temperature improves height replication of the microstructure of light guide plates. Optimal mold temperature to maintain flatness and increase microstructure replication of light guide plates is 60°C. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers