The crude rice straw hydrolysate (RSH) produced by dilute acid hydrolysis contains toxic substances, which are inhibitory to microbial growth. Removal of these toxic compounds was achieved by ethyl acetate extraction to produce the extracted rice straw hydrolysate (Ext -RSH). The utilization of the fermentable sugars of RSH as well as Ext -RSH by A. terreus was determined in batch culture fermentation. The Ext -RSH gave a marked improvement in fermentability over the crude RSH. The presence of toxic materials in crude RSH resulted in a long fermentation time (120 h) but this value was 60 h in the Ext -RSH medium. The productivity of biomass increased 3-4 times after extraction of the inhibitory substances from RSH. The effect of crude inhibitors extract on biomass production was tested by the standard inhibition assay and showed complete inhibition when it was added to the Ext -RSH culture medium at a concentration of 20  g/l. Monod model was developed to describe the cellular growth of A. terreus in RSH medium. The model included inhibition term for toxic agent in RSH. The agreement between the experimental data and the model predictions demonstrated the adequacy of the proposed models.