Topochemical engineering of fiber Surfaces is an attractive strategy to fabricate a product with desired Surface properties especially by using reactions with organic molecules in aqueous medium. In this study, the bagasse soda pulp was treated with carboxymethyl cellulose (CMC) in order to introduce more charged groups on the Surfaces of fibers. The carboxymethylation of fiber Surface was carried out under temperatures of 85, 95, and 120° C at 60, 90 and 120 minutes in the presence of calcium chloride as an electrolyte. The drainage time, water retention value (WRV), tensile index, and burst strength of CMC-modified pulps were measured and compared with corresponding values of untreated pulp and CMC-treated pulps by conventional methods. The results indicated that the treatment of fibers with CMC markedly increased the tensile index and burst strength of the modified pulp handsheets in comparison with unmodified pulp ones. The maximum strength properties were achieved at the reaction conditions of 120 ᵒ C and 90 min between fiber and CMC. However, drainage time was not impaired by modification of the pulp. Water retention value of CMC-modified pulps decreased unexpectedly in some conditions. Further characterization using FTIR spectroscopy and XRD demonstrated hydrogen bonding development and a slight decrease in crystallinity due to fiber modification process. It is concluded that introducing acidic groups via topochemical modification of bagasse fiber Surfaces may influence the most properties of the final pulp.