In the present study, effect of particle size and alkaline pretreatment of five recorded lignocellulosic wastes on production of xylanase by five fungal isolates was studied. The different raw substrates used were wheat bran, saw dust, maize straw, rice straw, sugarcane baggase. These raw substrates were firstly subjected to different alkali pretreatments (0.5N NaOH, 0.1N NaOH, and 1.0N NaOH) and added to the culture medium for xylanase production. Maximum xylanase production was achieved with 0.5N NaOH pretreated raw substrates as compared to untreated raw substrates in all five fungal isolates. The 0.5N NaOH treated five raw substrates were then passed through 0.2mm, 0.5mm, 0.8mm, 1.4mm and 2.0mm sieves and used for xylanase production . Raw substrates of 0.8mm particle size supported maximum xylanase production in all five fungal isolates. The xylanase activity increased significantly in Chrysosporium tropicum, Aspergillus fumigatus and Aspergillus terrus from untreated maize straw to 0.5N NaOH and 0.8mm size treated maize straw, the corresponding values increased from 0.204±0.002, 0.118±0.001 and 0.030±0.005 to 0.448±0.004, 0.415±0.002 and 0.441±0.008 μmoles of xylose/min/ml of culture filtrate, respectively. Malbranchaea sp and Emericella nidulans also exhibited significantly higher xylanase activity with wheat bran, the corresponding values increased from 0.040±0.012 and 0.138±0.003 to 0.513±0.005 and 0.390 ± 0.002 μmoles of xylose/min/ml of culture filtrate, respectively.