: The soil weed seed bank is the source of future weed infestations. Seed predation can result in a large number of seed losses, thus contributing to weed biocontrol. Earthworms are important predators of seeds and seedlings and affect their survival after gut passage. A study was conducted to assess the ability of Pheretima guillelmi (Kinberg) to ingest and digest the seeds and seedlings of fifteen main farmland weed species. Pheretima guillelmi ingested the seeds and seedlings of each weed species tested. The percentages of seeds and seedlings ingested by the earthworm were 96.7 to 100% and 21.7 to 94.2%, respectively. The earthworm showed greater ingestion of seeds than seedlings for each species. Pheretima guillelmi also digested the seeds and seedlings of each weed species tested to varying extents. The percentages of seeds and seedlings digested by the earthworm were less than 15% irrespective of the weed species. Passage through the gut of Pheretima guillelmi affected the survival of seeds and seedlings. The germination of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], Chinese sprangletop [Leptochloa chinensis (L.) Nees], Mexican sprabgletop [Leptochloa fusca (L.) Kunth], redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], and ricefield flatsedge (Cyperus iria L.) seeds egested by the earthworm decreased by 46, 49, 47, 25, 38, 26, 32, 13, and 15%, respectively, compared with the respective control seeds. In contrast to seed ingestion, ingestion of seedlings by Pheretima guillelmi was fatal to the individual for each species. No seedlings could survive after gut passage through the earthworm. Our results indicate that predation of weed seeds and seedlings by Pheretima guillelmi probably depletes the soil weed seed bank and that the introduction of Pheretima guillelmi into fields is a potential strategy for weed biocontrol in farmland.