We report two cases of familial juvenile polyposis coli. SMAD4 gene mutation was found in our two patients, leading to the definite diagnosis. Colonic cancer occurred in the first patient. Long-term outcome was favorable after colectomy. In the second patient, prophylactic total colectomy was performed. Rectal bleeding, diarrhea, stomach obstruction and vomiting developed during the follow-up. Proctectomy, distal partial gastrectomy and total gastrectomy were successively performed.