Periprosthetic joint infection is one of the major complications of joint replacement. In hip joint replacement, since dislocation and loosening have been clearly decreased with progress in surgical techniques and the use of appropriate devices such as large-diameter heads and cross-linked polyethylene, implant-related infection has become the most challenging complication affecting outcomes after surgery. The cause of implant-related infection is the formation of the biofilms that cover the bacteria with polysaccharide barriers. Because the biofilm protects the bacteria from antibiotics and immune reaction, biofilm makes infection more serious. We developed a new hip joint prosthesis with Ag-HAp coating and launched it in Japan in 2016. To apply this technology to various situations, it is important to understand the relationship between the antibacterial ability and the elution behavior of silver ions. In this study, we aimed to clarify the relationship between antibacterial activity, the crystal structure of HAp, and the elution behavior of silver ions. Ag-HAp-coated titanium specimens with various crystallinity were prepared for this study. The Ag-HAp layer was accumulated by flame spraying and crystallized by vacuum heat treatment or hydrothermal treatment. An elution test and antibacterial test with bovine serum were performed. A film adhesion test modified from ISO 22196 was performed to evaluate the antibacterial activity against various species. It was confirmed that Ag-HAp was effective in various bacterial species, including methicillin-resistant Staphylococcus aureus. Moreover, it was also confirmed that the elution property and antibacterial activity could be controlled by the changes in the crystallization method and the surface coverage of microcrystalline HAp. Moreover, antibacterial activity depended on the kinds of media. It is expected that the implant with Ag-HAp coating can contribute to the reduction of postoperative infection risk.