A series of new isoxazolidines was prepared by 1,3-dipolar cycloaddition of different mono-substituted styrenes with 1,3-dipolar compounds that were prepared by the reaction of N-methylhydroxylamine sulfate with aromatic carbonyl substances. This synthetic pathway for the preparation of isoxazolidines was an ideal process of green chemistry. The synthetic products were 5-substituted isoxazolidines and their structures were characterized by mass and NMR (1H-, 13C-, COSY, HSQC, and DEPT) spectrometry, and their bioactivity was investigated indicating that some new compounds inhibited Botrytis cinerea effectively.