Two experiments were carried out from Feb to Aug, 2017 at the laboratory and the experimental farm of Can Tho University to investigate nutrient contents and in vitro digestibility values of rice straw after it's use to cultivate mushrooms and to evaluate the effect of rice straw enriched by urea, molasses and minerals on in vivo digestibility and nutrient intake of cattle. In Experiment 1 a complete randomised design was used for the in sacco evaluation of rice straw at three stages: initial (R), at 20 days treated with water (RW20) and after harvesting mushrooms (MS). There were 8 replicates of each treatment. Faeces of a Murrah buffalo were used as inoculant. In Experiment 2, four Red Sindhi crossbred cattle (138 ± 12 kg) were allocated in a 4 x 4 Latin Square design to four diets, which included rice straw (R), rice straw plus urea-molasses-mineral mixture (RS+UMM), urea-treated rice straw (URS) and urea-treated rice straw plus molasses-mineral mixture (URS+MM). The crude protein and ash in MS was higher and NDF lower than in R and RW20. In vitro digestibility values at 24 h were similar but were lower for MS at 96 h.The MS after drying was dark, dusty and had a bad smell and was not palatable to cattle. In Experiment 2, adding urea, molasses and minerals to rice straw, or molasses and minerals to urea-treated rice straw, increased intake, DM in vivo digestibility and N retention.