Abstract: This paper reports on the results of spraying with suspensions of pirimiphos-methyl (2g/m2) and decamethrin (50mg/m2) in experimental huts fixed with window-trapsduring July-October 1982 in the Tangkou People's Commune, Jining County. The results showed that pirimiphos-methyl could effect 50% mortality 'of intrusive A. sl-nensis mosquitos for more than 41 days after spraying, while decamethrin could maintain 50% mortality for two months and more. The residual effectiveness of pirimiphos-methyl on walls could last 24-54 days after spraying and its fumigation activity up to 30 days. The residual effectiveness of decamethrin on most kinds of walls could last more than three months, but it had no fumigation activity. For pirimiphosmethyl no evident repellency was noticed, while for decamethrin an enhanced irritability was found. Both insecticides are safe for use and worth further testing ih field application.