Intestinal capillariasis is an emerging fish-borne helminthic disease caused by the round worm Capillaria philippinensis. Chronic infection may lead to death if the disease is misdiagnosed and inappropriate treatment is given. We used a rapid lateral-flow immunochromatographic test for screening of intestinal capillariasis in patients with chronic diarrhea. We screened 292 chronic diarrhea patients who had visited hospitals in Thailand. Sixty-six (22.6%) cases were positive according to the kit. All positive patients received mebendazole at 200 mg twice per day for 30 consecutive days or albendazole at 200 mg twice per day for 10 consecutive days. Later, stool concentration techniques, used to examine stool samples from all serologically positive individuals on three consecutive days, revealed C. philippinensis eggs, larvae, and/or adults. The kit is useful for screening and rapid diagnosis of intestinal capillariasis in chronic diarrhea patients in an endemic area for prevention of serious disease and facilitates treatment.