The surgical instrument (1) for colon-rectum operations comprises: - a handle (2), - a shaft assembly (G) that frontally protrudes from the handle, - a first head (3) that frontally protrudes from the shaft assembly (G) comprising a mechanical stapler of 'cut-and-sew' type and adapted to cut and suture the colon-rectum; - a second head (4) that frontally protrudes from the shaft assembly (G) disposed at the side of the first head (3), comprising forceps adapted to tighten and strangulate the colon-rectum without cutting it; wherein the shaft assembly (G) and the first and the second heads (3, 4) are dimensioned in such manner to be inserted into a cannula of a trocar for laparoscopy, and where the forceps of the second head (4) comprise a plurality of nozzles (U, U') connected to at least a duct (47, 47') formed in the second head (4) and communicating with a main duct (75) formed in the shaft assembly (G) connected to a supply unit (B) adapted to supply a washing liquid that comes out of the nozzles (U, U') to wash the colon-rectum stump from top to bottom, said nozzles (U, U') being configured so as to pierce the wall of the colon-rectum, but not cross the colon-rectum from side to side.