The study evaluated the anthelmintic resistance status of gastrointestinal nematodes in sheep flocks in São Paulo State, Brazil, and compared it to previous surveys. The research involved 15 sheep farms, each with at least seven animals, treated with various anthelmintics: albendazole, levamisole, ivermectin, monopentel, closantel, and moxidectin. The fecal egg count reduction test (FECRT) was used to assess the efficacy of each anthelmintic. Haemonchus spp. was the most prevalent nematode, and the mean efficacy of albendazole was 40%. Levamisole showed high efficacy in two farms (90%), while ivermectin and moxidectin had the lowest efficacy (34% and 21%, respectively). Closantel demonstrated low efficacy (63%), and monopentel had an overall mean efficacy of 79%, being the only anthelmintic with efficacy >95% in five farms. The results indicated that all 15 sheep herds had multiple anthelmintic-resistant gastrointestinal nematodes. The study highlights the increasing resistance to various anthelmintic compounds and emphasizes the need for sustainable and long-lasting methods to prevent gastrointestinal nematode infections in sheep husbandry.The study evaluated the anthelmintic resistance status of gastrointestinal nematodes in sheep flocks in São Paulo State, Brazil, and compared it to previous surveys. The research involved 15 sheep farms, each with at least seven animals, treated with various anthelmintics: albendazole, levamisole, ivermectin, monopentel, closantel, and moxidectin. The fecal egg count reduction test (FECRT) was used to assess the efficacy of each anthelmintic. Haemonchus spp. was the most prevalent nematode, and the mean efficacy of albendazole was 40%. Levamisole showed high efficacy in two farms (90%), while ivermectin and moxidectin had the lowest efficacy (34% and 21%, respectively). Closantel demonstrated low efficacy (63%), and monopentel had an overall mean efficacy of 79%, being the only anthelmintic with efficacy >95% in five farms. The results indicated that all 15 sheep herds had multiple anthelmintic-resistant gastrointestinal nematodes. The study highlights the increasing resistance to various anthelmintic compounds and emphasizes the need for sustainable and long-lasting methods to prevent gastrointestinal nematode infections in sheep husbandry.