Background: A computer-aided diagnosis system for bone scintigraphy using semiquantitative index [Bone Scan Index (BSI)] has been used to measure the tumor burden of bone metastases. We examined relationships of BSI, bone turnover marker, and prostate-specific antigen (PSA)-progression free survival (PFS) after docetaxel-treatment for castration resistant prostate cancer (CRPC) with bone metastasis. Methods: Sixteen CRPC patients with bone metastases (median age 72, range 52 to 82) were treated with docetaxel. We evaluated bone metastasis by bone scintigraphy before or around six months after docetaxel-treatment retrospectively. BSI was automatically calculated by BONENAVI software version 1 (FUJIFILM RI Pharma, Co. Ltd., Tokyo, Japan; Exini Bone, Exini Diagnostics, Sweden). Serum PSA, bone alkaline phosphatase (BAP), carboxyterminal telopeptide of type I collagen (I-CTP) were examined every months. PSA-PFS was evaluated after docetaxel-treatment and compared with baseline of BSI, BAP, I-CTP, and change of these value after treatment. Overall survival (OS) was also evaluated by these markers. The rate of patients with PFS and OS was estimated by the Kaplan-Meier method. Results: Baseline of BSI, the serum BAP, and I-CTP before docetaxel-treatment did not affect PFS. The change of BAP and I-CTP by the docetaxel-treatment also did not affect PFS. Only the change of BSI affected PFS and the median PFS of CRPC patients with increased BSI and decreased BSI was 5.5 months and 10 months, respectively (p=0.026). Although OS showed a longer tendency in CRPC patients with decreased BSI than with increased BSI, there was not the significant difference (p=0.12). Conclusions: The change of BSI affected PFS in CRPC patients with bone metastases. Bone scan and its evaluation with BONENAVI was effective to monitor the clinical course during chemotherapy.