We have previously reported the insecticidal activity of some 4H-1,3,2-benzoxazaphosphorines (BOPs) with no substituent on the benzene ring. This paper deals with the insecticidal activity of 31 kinds of BOP-2-thiones (V), which were synthesized to examine the substituent effects at the 2, 3, 6, and 8 positions of BOP. Schiff bases prepared from the corresponding salicyl aldehydes and amines were reduced by sodium borohydride to give N-alkyl 2-hydroxybenzylamines. 2-Ethoxy-BOP-2-thiones were prepared using commercially available ethyl dichlorothiophosphate (procedure 1), while 2-methoxy and 2-propoxy-BOP-2-thiones were synthesized via procedure 2. A bioassay was conducted on Spodoptera litura and Laodelphax striatellus. The results showed that BOP-2-thiones with no substituent on the benzene ring (1-6) were fairly active against both insects. There was little relationship between insecticidal activity and substituents at the 2 and 3 positions, but 2-n-propoxy derivatives seemed less active. The introduction of a chlorine or bromine atom at the 6-position generally resulted in a decrease of activity, though compounds 19 and 20 (6-bromo/chloro-3-isopropyl-substituted) were exceptionally insecticidal and the most active in the series (though less active than malathion and propoxur). The 6-nitro derivatives (28-31) were completely inactive. Since 19 and 20 had fairly high insecticidal activity and BOPs have many possibilities for modification, they can be considered as interesting lead compounds.