The residual efficacy of a relatively new pyrethroid, betacyfluthrin was compared with DDT against Anopheles sinensis Wiedemann in some village houses in Penang, Malaysia, for a period of 30 weeks. Efficacy was determined by exposing laboratory-cultured An. sinensis mosquitos to treated wall surfaces with either betacyfluthrin at 15 and 25 mg/m2 or DDT at 2,000 mg/m2 for one hour. Betacyfluthrin provided a longer residual effect (up to 210 days with > 70% mortality) compared with DDT. The potential of betacyfluthrin as a candidate for residual spraying for malaria control is discussed.