Rainbow trout were fed two experimental diets differed in lipid content by replacement of crudestarch (lipid-poor diet : 4.2% lipid or lipid or lipid-rich diet : 14.8% lipid) supplemented or not with antibiotics (a combination Flumequine + Gentamycin, 1:4). The apparent digestibility of dry matter, crude protein, lipid, carbohydrate and total energy were measured. Addition of lipid by replacement of crude starch in the fish diet in the absence of antibiotics enhanced significantly (p < 0.01) the apparent digestibility of dry matter, crude protein, carbohydrate and total energy, but did not influence those of lipid. Antibiotics supplementation of the lipid-poor diet (consequently with a high level of carbohydrate) enhanced significantly (p < 0.01) the apparent digestibility of dry matter, crude protein, lipid, and total energy, but not those of carbohydrate. On the other hand the antibiotics-treated lipid-rich diet (consequentlywith a low level of carbohydrate) showed a higher (p < 0.01) digestibility for dry matter, lipid, carbohydrate and total energy, but not for crude protein. The stimulatory effect of antibiotics on nutrient digestibility is discussed.