Objective. Bacterial infection is a serious complication after joint replacement surgery. In particular, methicillin-resistant Staphylococcus aureus (MRSA) and epidermidis(MRSE) are very difficult to eradicate in infected prosthetic joint. Therefore, the retention rate of initial prosthesis affected with such resistant microorganisms is still low. Gentian violet shows potent antibacterial activity against gram-positive cocci as minimal bactericidal concentration is less than 0.1 %. In the present study, we investigated the efficacy of treatment with gentian violet against MRSA and MRSE infections after THA, TKA, and bipolar hip hemiarthroplasty (BHP). Methods. There were 8 patients in this study; five patients with deep periprosthetic MRSA infection (2 THA, 2 BHP, 1 revision TKA); 3 patients with MRSE infection (1 revision THA, 1 BHP, 1 TKA). When infection was suspected after the surgery, we quickly obtained synovial fluid and periprosthetic soft tissue from the joint and applied to culture and microscopic examinations for detection of microorganisms. After identification of bacterial species, we immediately debrided the affected joint and washed thoroughly twice with 0.1% solution of gentian violet for 3 minutes each, followed by intra-articular multiple injection of arbekacin sulfate solution. Then we inserted an aspiration tube into the joint and administered appropriate antibiotics intravenously. If the inflammatory symptoms persisted in spite of the first treatment, we repeated the treatment until inflammation signs and intra-articular microorganisms could not be detected. Results. At first we examined the bactericidal activity of gentian violet solution against MRSA and MRSE by culture examination with or without the solution. We confirmed gram-negative bacillicould be alive but the both MRSA and MRSE could not be alive by the treatment with 0.01 % solution of gentian violet for 3 minutes. The treatment with gentian violet allowed subsidence of the infection in all patients. Furthermore, we could preserve 4 prostheses with MRSA infection; 1 THA, 1 revision TKA and 2 BHPs; 2 prostheses with MRSE infection; 1 TKA, 1BHP. However, we could not preserve 2 prostheses, 1 THA with MRSA infection and 1 revision THA with MRSE infection. Thus, the prosthetic retention rate of this study for MRSA and MRSE infections was 75 %. We performed two-stage operation for the 2 patients in whom we could not preserve the prostheses as follows: after excision of the infected total hips followed by successful reimplantation. Moreover, all of the patients in this study are able to keep the walking ability after joint replacements. Conclusion. Infection of methicillin-resistant Staphylococcus species after joint replacement surgery has tended to increase. Gentian violet exerts a potent antibacterial activity against such microorganisms at the concentration of less than 0.1 %. We obtained good retention rate by the treatment using gentian violet against MRSA and MRSE infections after the joint surgeries. In addition, both MRSA and MRSE have not showed drug resistance for gentian violet. Therefore, we suggest that gentian violet will become a promising adjunct agent for infection after joint replacement surgery not only methicillin-sensitive but also methicillin–resistant Staphylococcus species