This experiment was aimed to investigate the effects of paraformaldehyde on activities of digestive enzymes of rumen and nutrient digestion in cattle. Four of Xinjiang brown×Simmental F₁ non-pregnant cattle, 2-year-old, with body weight of (283.5±5.4) kg, were fitted with permanent ruminal fistula, and were fed a diet with a ratio of 4:6 of concentrate to roughage ad libitum. By 4×4 Latin square design, each animal was supplemented with paraformaldehyde (PFD) at the additive amount of 0 (control), 150, 300 and 600 mg/kg, respectively in each phase. The results showed that the dry matter voluntary intake of cattle was up-down changed with PFD supplementation, and was the highest at the PFD additive amount of 300 mg/kg, increasing by 25.6% (P<0.01) compared with the control group. The activities of ruminal endocellulase, exocellulase, cellobiase and xylanase were up-down changed with the increasing of PFD additive amount, and were the highest at the PFD additive amount of 300 mg/kg, increasing by 38.1% (P<0.01), 37.0% (P<0.01), 45.9% (P<0.01) and 25.0% (P<0.05), respectively. However, adding PFD had no significant effect on the activities of pectinase, amylase and protease (P>0.05). The apparent digestibility of dry matter, organic matter and cellulose, rather than crude protein, decreased significantly by PFD supplementation (P<0.05). However, the amounts of digested dry matter, organic matter, crude protein, cellulose and energy were up-down changed with PFD supplementation, being the highest at 300 mg/kg, by 18.5% (P<0.01), 18.7% (P<0.01), 20.4% (P<0.01), 17.9% (P<0.01) and 14.6% (P<0.01). The retention of nitrogen, calcium and phosphorus also were up-down changed with PFD supplementation, being the highest at 300 mg/kg, by 66.1% (P<0.01), 19.3% (P<0.01) and 16.2% (P<0.01), respectively. It is concluded that supplementation with PFD (300 mg/kg diet) increases the activities of ruminal cellulase, voluntary feed intake, the digested amounts of diets, and the nitrogen retention, so being beneficial for digestion and nutrition of cattle.