To evaluate the effect of formic acid based preservative (FAP) on fermentation, aerobic stability and nutritive value of whole-crop wheat silage, wheat was harvested at early dough stage and ensiled for 90 d with 0, 2 3 and 4 ml/kg FA.P. The FAP treatment did not affect the concentrations of lactic and acetic acid but increased formic and propionic acid and decreased concentrations of butyric acid, ethanol, ammonia-N and gas losses of the silages. Under aerobic conditions, FAP treated silages had lower pH, CO2 production and the numbers of yeasts (except FA2) and moulds than the control silage (P<0.05). Contents of neutral detergent fiber, acid detergent fiber, acid detergent lignin and cellulose decreased in the FAP treated silages, but 96 h in vitro gas production and in vitro organic matter digestibility of the silages were not affected by FAP treatment. Applying 4 ml/kg FAP on wheat silages was most effective.