A Summary The appropriate time to initiate bisphosphonate treatment after a fragility fracture has not yet been established. In this study, we found no significant differences in short-term functional recovery between femoral neck fracture patients who received bisphosphonate treatment at 2 versus 12 weeks after hemiarthroplasty. Introduction Bisphosphonate is the mainstay therapy for prevention and treatment of osteoporosis. The aim of this study was to investigate the effect of bisphosphonate initiation on short-term functional recovery in femoral neck fracture patients at 2 versus 12 weeks after hemiarthroplasty. Methods One hundred patients were randomly allocated into two groups in a parallel group designed, randomized, controlled trial. Both groups received risedronate 35 mg/week at either 2 or 12 weeks after hemiarthroplasty. All patients received calcium and vitamin D supplementation. Functional recovery was assessed by de Morton Mobility Index, Barthel Index, EuroQol 5D, visual analog scale, 2-min walk test, and timed get-up-and-go test at 2 weeks, 3 months, and 1 year after surgery. Results At the 3-month follow-up, all functional outcome measures showed significant improvement in both groups. There were no statistically significant differences in any of the functional outcomes between groups at both the 3-month and 1-year follow-ups. Although patients who received bisphosphonate initiation at week 2 had lower serum calcium level at 3 months and more overall adverse events than patients in the week 12 group, no patients in either group discontinued their prescribed medications. Conclusions While underpowered, the findings of this study suggest that there were no significant differences in short-term functional recovery or significant adverse events between the two bisphosphonate groups. Thus, the initiation of bisphosphonate therapy may be considered as early as 2 weeks after femoral neck fracture. It is important that low serum calcium and vitamin D status must be corrected with calcium and vitamin D supplementation prior to or at the time of bisphosphonate initiation. Clinical trial registration number This study was registered in the database via the Protocol Registration and Results System (PRS) (NCT02148848).