A growing number of biomaterial-associated infections cause bone implant failures in early and long-term applications. In this regard, a calcium silicate-gelatine composite bone implant with high strength and superior osteogenic activity was coated with a layer of Ag, chitosan polysaccharide (CS) or water-soluble chitosan oligosaccharide (COS) as a bactericidal agent. The influences of surface modifications to the bone implants on phase composition, microstructure, antibacterial effectiveness, and osteogenic activity in vitro were evaluated. Experimental results revealed the presence of the coating on the implant surface using a simple deposition technique. The in vitro antibacterial evaluation indicated that the antimicrobial effectiveness of the Ag coating against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) was inferior to the 0.4% CS coating, but comparable to those of 0.2% CS and 0.4% COS coatings after 48 h of culture. CS presented a greater bactericidal effect than COS, which was bacteria-independent. CS and COS coatings had no significant cytotoxicity towards L929 cells at coating concentrations of 0.1%, 0.2%, and 0.4%, except for the cells exposed to the 0.4% CS coating, while the 0.004% Ag coating remarkably produced cytotoxicity. The assays of cell functions consistently showed significantly higher osteogenic activity of MG63 cells grown on CS and COS-coated surfaces by increased attachment, proliferation, alkaline phosphatase, osteocalcin, and calcium deposits production, except for the 0.4% CS coating, in comparison with those on the Ag coated surface. It was concluded that, taking antibacterial ability and osteogenic activity into account, 0.2% CS-coated and 0.4% COS-coated calcium silicate-gelatine composite bone implants had a large potential to be used in bone grafts and fracture fixation devices.