Fermentation of oak leaves with Sporotrichum pulverulentum decreased the contents of total phenols and condensed tannins by 58 and 66% respectively in 10 d. The protein precipitation capacity decreased by 65%. Further increase of fermentation time up to 40 d did not increase substantially, the tannin degradation. Following fermentation, neutral detergent fibre, acid detergent fibre, hemicellulose, cellulose and lignin decreased by 12–16%, 8–10%, 31–51%, 0.3-3% and 14–15% respectively. The loss in dry matter was from 17–21%. The in sacco dry matter digestibility of the fermented leaves was 17% compared to 27% for the unfermented leaves.