A 67-year-old man was refered to our institution with a complaint of elevated serum prostate-specific antigen (PSA) level (54 ng/mL). Diagnosis was adenocarcinoma of the prostate with a Gleason score of 9, with bone metastasis (stageD2). He was treated with maximal androgen blockade followed by estramustine phosphate (EMP) because of the progression to hormone-refractory prostate cancer (HRPC). Leukocytosis over 20000/μL was repeatedly observed at each administration of EMP. This is the first case report of leukocytosis in response to EMP in an HRPC patient. The present case suggests that EMP could modulate leukocyte differentiation in HRPC patients.