The association of linseed and nitrate decreases enteric methane (CH4) emission in dairy cows, but has not been studied in fattening cattle for animal performance, CH4 emission, animal health and presence of residues in beef. To address these questions, 16 young Charolais bulls received from weaning at 9 months to 14 months a control diet (C), then were split in 2 groups of 8 balanced for CH4 emission, dry matter intake (DMI) and liveweight gain (LWG). They received during 2 months either C diet or a diet supplemented with extruded linseed and calcium nitrate (LN); they were then slaughtered. The C diet contained 67% wrapped haylage and 33% concentrate mainly made of maize, wheat and rapeseed meal. In LN diet, rapeseed meal and a part of cereals were replaced by 35% extruded linseed and 6% calcium nitrate; linseed fatty acids and nitrate supply in the diet was 1.9 and 1.0%, respectively. Methane emission was measured continuously using the Greenfeed system. Methaemoglobin was determined in peripheral blood every week for bulls receiving the LN diet. Nitrate and nitrite concentrations were determined in rumen, liver and tongue sampled at slaughter. Total DMI did not differ between diets (11.0±1.2 kg/d on average, P>0.05) but concentrate intake was lower for LN due to refusals, so that LWG was higher for C than for LN (1.60 and 1.26 kg/d, respectively, P=0.013). Daily CH4 emission was lower by 10% for LN than for C (241 and 269 g/d, respectively; P<0.001), but CH4 emission per kg DMI or per kg LWG did not vary (P>0.05). Methaemoglobin was under detection limit for most animals (<2% of total haemoglobin), and always lower than 5.6%, suggesting the absence of risk for animal health. Nitrite and nitrate concentrations in offal did not differ between diets. In conclusion, a moderate supply of linseed and nitrate in bulls resulted in a moderate decrease in daily enteric CH4 emission without adverse effects for animal health and food safety.