The effects of three variables; polysaccharidase inclusion level (0, 5 and 10 g/kg), moisture content (500, 600 and 700 g/kg dry matter (DM), and particle size (20, 5 and 2 mm), on the quality and degradation characteristics of ensiled rice straw were investigated. The polysaccharidase product used was shown to contain a broad spectrum of activities against polysaccharides typical of plant material. The major activities present being: mixed link glucanase, xylanase and both endo- and exo-cellulase. The straw treated with polysaccharidase had a lower final pH (5·21, 4·87, 4·82; P < 0·01), higher concentrations of lactic acid (1·98, 3·90, 3·67 g/kg; P < 0·01), a lower content of neutral-detergent fibre (689, 630, 621 g/kg DM; P < 0·01) and a higher solubility, measured as washing losses from nylon bags (152, 196, 212 g/kg DM; P < 0·01) for the 0, 5 and 10 g/kg polysaccharidase treatments respectively. The samples were subsequently incubated in nylon bags in the rumen of three 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 increased (P < 0·01) by the addition of polysaccharidase. The maximum potential degradability (a + b), however, was not altered by any of the treatments. The values for c were 0·0498, 0·0677 and 0·0817 per h and for (a + b) were 62·4, 62·1 and 62·8 g/100 g DM for the 0, 5 and 10 g/kg polysaccharidase enzyme additions respectively. It is concluded that the use of polysaccharidase enzymes can assist in the preservation of wet straw and can result in improved degradation characteristics.