Poplar chips were pre-treated by Trametes versicolor for 1, 2 and 3 weeks. Pre-treated chips, after washing, have been air dried for kraft pulping to achieve pulp kappa number of about 20. Pulp samples have been analyzed by Bauer Mc Nett, Kajaani analyzer and SEM. The results indicated that fungi pre-treatment of chips can degrade lignin and carbohydrates and affect kraft pulping and fiber characteristics. Higher chemical charge in pulping, lower fine and higher long fiber fraction were observed in pre-treated pulp samples in comparison with others. Fiber length, cross sectional area, width, cell wall thickness and volume index were increased by increasing pre-treatment time while fine length, fiber coarseness and curl have been reduced. Based on the study findings, with respect to higher fiber length, lower fine, and lower fiber curl and coarseness, 2-weeks pre-treatment of chips was recommended to produce acceptable overall fiber properties in kraft pulping. (C) 2010 Elsevier Ltd. All rights reserved.