Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) is a common parasitoid of aphids including the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). To maximize the use of A. gifuensis for biological control of M. persicae, the functional response of A. gifuensis using M. persicae as a host was determined at 4 constant temperatures (15, 20, 25, and 30 °C) and 20 host densities (5, 10, 15, increased incrementally by 5, to a maximum of 100) on a 6-leaf sweet pepper plant (30 cm in height) over a 24 h period. Roger's random parasitoid equation (RRPE) and Holling's disc equation (HDE) were used to fit the data. The results showed that functional responses at all temperatures were type II, and the instantaneous attack rate (a) in both models increased as temperature increased from 15 to 25 °C and then decreased at 30 °C. The highest instantaneous attack rate (a) for A. gifuensis was at 25 °C for the 2 models, 1.3203 ± 0.0415 d^-1 for HDE and 4.295e 03 d^-1 for RRPE. The handling time (T_h) for A. gifuensis by HDE was between 0.0105 ± 0.0002 d at 20 °C and 0.0214 ± 0.0009 d at 30 °C and by RRPE was between 1.265e-02 ± 3.808e-04 d at 20 °C and 0.0218 ± 0.0010 d at 30 °C. Aphidius gifuensis achieved its highest parasitism rate at medium temperatures. The results from this study showed that A. gifuensis performed best at 20 °C, suggesting that this parasitoid will be more effective as a biological control agent for M. persicae when the temperature is under 30 °C.