Since the outbreak of COVID-19, disposable face masks have been widely implemented as a powerful preventive measure to minimize the transmission of the virus. Despite its high usage, however, studies on the effects of disposed face maskes on soil ecosystems are limited. This study aims to investigate the toxicological effects of microplastics from the masks on Caenorhabditis elegans (C. elegans) in soil media. Effects of microplastics from three types of disposable face masks (KF94 mask, medical mask, and particulate respirator) and a reference material for polypropylene (PP) on the growth and number of offspring of C. elegans were assessed. The growth of C. elegans was not influenced by exposure to the microplastics. On the other hand, significant decreases in the number of C. elegans offspring were observed under exposure to 0.3% (microplastic/soil, w/w) microplastics from KF94 mask and particulate respirator. MS-based metabolomic analysis showed distinct metabolic alterations between different masks, which could not be detected in the phenotypes. The polyamine biosynthesis pathway of C. elegans was commonly affected by both KF94 mask and particulate respirator, but dissimilar metabolic changes were observed between them. Ultra high resolution MS of plastic additives in the masks implicated that the differential metabolic changes could be ascribed to different plastic additives with reproductive toxicity to C. elegans, such as phthalates.