Laboratory strains of Culex pipiens molestus Forskal and Culex tritaeniorhynchus Giles from northern Taiwan were compared for their susceptibility to the Sanhsia MQ1–2 (SH) strain of Japanese encephalitis (JE) virus isolated from Taiwan. After feeding on a sweetened blood–virus mixture, viral titers in Cx. p. molestus during the 14-d incubation period ranged from a minimum of 2.9 log₁₀PFU (plaque forming units) per mosquito on day 3 after ingestion to a maximum of 4.65 log₁₀PFU at day 8 and in Cx. tritaeniorhynchus from 2.6 on day 10–5.18 log₁₀PFUper mosquito on day 13. Although virus titer in Cx. p. molestus was lower than in Cx. tritaeniorhynchus at the end of the experiment, this difference was not statistically significant. The median infective dose (ID₅₀) for Cx. p. molestus was 2.83 log₁₀PFU and for Cx. tritaeniorhynchus was 1.02 log₁₀PFU per mosquito, and this difference also was not significant. There also was no significant difference between the median infective dose for transmission (TID₅₀) per mosquito for Cx. p. molestus (5.34 log₁₀PFU) and Cx. tritaeniorhynchus (4.59 log₁₀PFU). We concluded that Cx. p. molestus is an effective laboratory vector of JE virus.