Mature fine tailings need to be dewatered to reduce the environmental impact caused by oil sands extraction. Polymer flocculants are commonly used to accelerate this process. In this work, we modified chitosan, a naturally occurring biopolymer, with 3-chloro-2-hydroxypropyltrimethylammonium chloride (Chito-CTA) and also grafted polyacrylamide to chitosan (Chito-g-PAM). We compared the dewatering performance of these two flocculants with that of a commercial cationic polyacrylamide (C-PAM). Chito-CTA and Chito-g-PAM dewatered tailings at rates of 18.27 and 20.72 m/h, respectively. The dewatering ability of Chito-CTA and Chito-g-PAM, measured in terms of capillary suction time (CST), was below 10 s, whereas the value for C-PAM was 82.3 s at optimum dosage. The turbidity of the supernatant obtained after flocculation with Chito-CTA or Chito-g-PAM was below 10 NTU, while C-PAM produced turbid supernatants. We studied the effect of flocculant microstructure on the specific resistance to filtration of the sediments. Chito-g-PAM produced sediments with the lowest resistance, 2.99 X 10(12) m/kg, while C-PAM's sediments had a much higher resistance of 40.26 X 10(12) m/kg. We also used the focused beam reflectance measurement technique to determine floc size evolution, floc stability, and time required to induce floc formation. Our results indicate that chitosan-based polymers may be successfully used to treat oil sands mature fine tailings.