Introduction We present tri‐modality therapy with i‐125 brachytherapy for high‐risk prostate cancer after holmium laser enucleation of the prostate. Case presentation A 75‐year‐old man had visited our hospital with complaints of dysuria. Holmium laser enucleation of the prostate was performed for benign prostatic hyperplasia. The resected histopathological prostate tissue showed malignancy (Gleason score: 3 + 3 = 6). Two years thereafter, Gleason score progressed (4 + 5 = 9) concomitantly with increased prostate‐specific antigen levels. Therefore, tri‐modality therapy, including brachytherapy, was applied. Combined androgen blockade therapy was conducted over a 9‐month period. One month after brachytherapy, external beam radiation was performed. Conclusion Brachytherapy following transurethral prostate surgery is relatively contraindicated because of increased adverse urethral event frequency and seed placement difficulties. A tri‐modality therapy, including brachytherapy, was implemented without any major problems in this patient with high‐risk prostate cancer after holmium laser enucleation of the prostate, following which he had a favorable prognosis without recurrence for 6 years.