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Diltiazem hydrochloride (DTZ) matrix tablets were prepared using polyacrylamide-grafted sodium alginate (PAam-g-SA) co-polymers having different percentages of grafting and their partially hydrolyzed products with a view to achieve sustained release of the highly water-soluble drug. PAam-g-SA co-polymers having different percentages of grafting were synthesized by free radical polymerization using acrylamide (Aam) as monomer and ammonium persulphate (APS) as initiator, and the resulting co-polymers were subjected to alkaline hydrolysis to produce their corresponding partially hydrolyzed co-polymers. Matrix tablets of DTZ were prepared by wet granulation using either PAam-g-SA co-polymers or partially hydrolyzed PAam-g-SA co-polymers. The effect of percentage grafting, drug load and calcium gluconate (CG), used as excipient, was studied in simulated gastrointestinal fluid. While the tablets prepared using the co-polymer having higher percentages of grafting provided faster drug release (100% in 5.5 h), the tablets prepared with the corresponding hydrolyzed co-polymer released the drug slowly (71% in 12 h). This behaviour in release appeared to be controlled by the relative magnitude of the viscosity and the swelling capacity of the copolymers. Moreover, increase in drug load tended to decrease the drug release from all types of tablets and increase in the amount of CG increased the drug release. FT-IR and DSC studies revealed the absence of any interaction between the drug and the co-polymers. The matrix tablet made of partially hydrolyzed graft co-polymer having the highest percentage of grafting provided the most sustained release of the drug.