Novel N-phosphinoyl heterocycles were synthesized by the reaction of a heterocycle against a phosphorochloridate in the presence of the strong base (n-BuLi or NaH). Studies on the structure-activity relationships were carried out as to acaricidal, aphicidal and nematicidal activities, respectively. With respect to the heterocycle portion, the acidity (pKa) of the parent heterocycles seems to control the pesticidal activities. It is also suggested that the unsymmetrical alkoxy(alkylthio)phosphinoyl structures with the proper length of alkyl groups are crucial to the high pesticidal activities. The effect of the chiral phosphorus atom was investigated as to 3-[ethoxy(sec-butylthio)phosphinoyl]-1, 3-thiazolidin-2-one. The levorotatory (-) isomer was shown to be more active against various pests.