Rice straw was ensiled in laboratory containers of 11 capacity. Three concentrations of moisture (50, 60 or 70%) 3 concentrations of a commercial cellulase enzyme preparation (0, 5 or 10g/kg dry matter (DM)) and 3 types of straw processing (2 cm, 5 mm or 2 mm length) were used. The preparations were stored at room temperature (approximately 20°C) for 30 days. The straw treated with cellulase had a lower final pH (5.21, 4.87, 4.82; P<0.05), higher concentrations of lactic acid (198, 383, 367 mg/100g; P<0.05), a lower content of neutral detergent fibre (689, 630, 620 g/kg DM; P<0.05) and a higher solubility, measured as washing losses from nylon bags (152, 196, 212 g/kg DM; P<0.05) for the 0, 5 and 10 g/kg cellulase treatments respectively. The samples were subsequently incubated in nylon bags in the rumen of 3 sheep for 8, 16, 24, 48 and 72 h to estimate degradation rate and potential degradability using the expression p+a+b(1-e-ct) where p is degradability at time t and a, b and c are constants. While there was no effect of moisture content or physical form of the straw, the degradation rate constant (c) was significantly increased (P<0.05) by the addition of cellulase. The maximum potential (a+b) however was unchanged. The values for c were 0.0496, 0.0677 and 0.0847/h-1 and the values for (a+b) were 624, 621 and 628 g/kg for the 0, 5 and 10 g/kg cellulase enzyme additions respectively. It is concluded that the use of cellulase enzymes can assist in the preservation of wet straw and can result in improved degradation characteristics.