This study aimed to assess the variability in respect of titer and properties of xylanase from Trichoderma reesei SAF3 under both solid-state and submerged fermentation. SSF was initially optimized with different agro-residues and among them wheat bran was found to be the best substrate that favored maximum xylanase production of 219 U (gws)(-1) at 96 h of incubation. The mycelial stage of the fungi and intracellular accumulation of Ca(++) and Mg(++) induced maximum enzyme synthesis. Inoculum level of 10 × 10(6) spores 5 g(-1) of dry solid substrate and water activity of 0.6 were found to be optimum for xylanase production under SSF. Further optimization was made using a Box-Behnken design under response surface methodology. The optimal cultivation conditions predicted from canonical analysis of this model were incubation time (A) = 96-99 h, inoculum concentration (B) = 10 × 10(6) spores 5 g(-1) of dry substrate, solid substrate concentration (C) = 10-12 g flask(-1), initial moisture level (D) = 10 mL flask(-1) (equivalent to a(w) = 0.55) and the level of xylanase was 299.7 U (gws)(-1). Subsequent verification of these levels agreed (97 % similar) with model predictions. Maximum amount of xylanase was recovered with water (6:1, v/w) and under shaking condition (125 rpm). Purified xylanase from SSF showed better stability in salt and pH, was catalytically and thermodynamically more efficient over enzyme from SmF, though molecular weight of both enzymes was identical (53.8 kDa).