Copolymers of acrylamide and cationic comonomers such as diallyldimethylammonium chloride can effectively dewater solid suspensions containing negatively charged fine particles. A good example of such suspensions is oil sands mature fine tailings (MFTs). However, little is known about the impact of the microstructure of copolymers in dewatering performance. In this study, we used a surface response methodology to systematically assess the impact of chemical composition and average molecular weight of poly(acrylamide-codiallyldimethylammonium chloride) in dewatering MFTs. We controlled the chemical composition and average molecular weight of the copolymers by manipulating feed monomer/comonomer ratios and initiator concentration. We found both the copolymer composition and the molecular weight averages were statistically significant variables for initial settling rates and supernatant turbidities of flocculated MFTs. However, capillary suction time and resistance to filtration depended only on copolymer composition and polymer dosage, not on average molecular weight. Depending on the polymer dosage, we found the optimum chemical composition to vary between 0 and 60 mol % acrylamide. The results of this study are important for the oil sands and polymer flocculation industry trying to use/produce flocculants at minimum cost and maximum performance.