[en] Microfibers (MFs) have recently become an increasingly prevalent pollutant in ecosystems and pose a direct threat to organisms and an indirect threat via adsorption of other pollutants. Here, we used Caenorhabditis elegans to study multigenerational effects of polyethylene terephthalate (PET) MFs (diameter 17.4 μm) by observing the maternal generation (P0) to the seventh offspring generation (F7) with continuous MF exposure. Exposure to 250-μm PET MFs decreased locomotion behavior and induced intestinal reactive oxygen species (ROS) in the P0 generation compared with other PET MF sizes. Moreover, no notably negative effects on survival were observed in any generation during continuous exposure to 250-μm PET MFs. However, the reproduction rate clearly decreased in the F2 and F3 generations but gradually recovered in the F4–F7 generations. Developmental abnormalities showed a close relationship with body length. Although some recovery was confirmed, there were significant decreases in body length in the F2–F5 generations. Interestingly, growth inhibition was also observed in the F6 generation without MF exposure. ROS production and dermal damage in the P0–F5 generations might have resulted in the toxicological responses. To the best of our knowledge, this is the first study to provide evidence of multigenerational toxicity of MFs in C. elegans.