This experiment was conducted to use spent cereals straw mixed with olive cake(SCO)and spent cereals straw mixed with tomato (SCT) from Pleurotus ostreatus mushroom as animal feed. In completely randomized design, twenty one male lambs, with initial weight 27±1.0 kg were allocated to three groups(1.untreated cereals straw (UCS), 2.Spent cereals straw with tomato pomace ( SCT) and  3.  Spent cereals straw with olive cake (SCO) ). The final live weight of the lambs received diets 1,2 and 3,44.4, 44.2 and 43. 3 kg respectively and their corresponding average daily gain were 191.0,189.0 and 178.0 g/day / animal. The average feed intake were 108.8, 107.0 and 97.0 kg in 90 days, respectively, which were significantly (p < 0.001) lower for SCO. Feed conversion ratio was 6.33, 6.32 and 6.51 respectively, which were not statistically different among the groups. This experiment showed that the spent compost of the cereals straw with olive cake and cereals straw with tomato pomace can be used only as a roughage in the lambs fattening diets.