A bioassay method was developed to use the parasporal crystal protein of Bacillus thuringiensis against plant-parasitic nematodes. Using this method, the parasporal crystal proteins of ten Bt strains showed activity against plant-parasitic nematodes. The toxicity of YBT-021 against Meloidogyne hapla, Pratylenchus scribneri, Tylenchorhynchus sp., Ditylenchus destructor and Aphelenchoides sp. was also assayed. The resulting LC50 values were 35.62 μg/ml, 75.65 μg/ml, 94.31 μg/ml, 215.21 μg/ml and 128.76 μg/ml, respectively.