This study is a continuation of the previous experimental analysis and is mostly focused on handsheet strength properties. Four completely different fibers, which were Hw-BKP, SW-BKP, White ledger, and OCC, were selected to investigate the effect of mechanical pre-treatment by Hobart mixer on handsheet strehgth properties. After equal time mechanical pre-treatment, the fibers were refined with laboratory valley beater for 10, 20 and 30 minutes, and handsheets were prepared from the fibers for physical strength comparison. Handsheets from SW-BKP and OCC showed 5-30% increase of breaking length, burst index, tear index, and compression index while handsheets from HW-BKP and White ledger no increase except tear index. In Hobart mixer pre-treatment, HW-BKP and White ledger fibers were easily attached to the wall of the mixer bowl and mechanical action was not effectively applied. The fiber length of Hw-BKP and White ledger were 0.837 mm and 1.591 mm, respectively, while SW-BKP and OCC were 2.744 mm and 2.033 mm, respectively, in weight weighted length. The effective mechanical pre-treatment seems to be related to the fiber length. Tear indexes of the pre-treated furnish were much higher than no pre-treatment at the same breaking length level.