Background: To evaluate the prognostic impact of time to castration resistance (TCR) in patients with metastatic hormone-naïve prostate cancer (mHNPC). Methods: We retrospectively evaluated 283 mHNPC patients with metastatic castration-resistant prostate cancer (mCRPC) who were initially treated with androgen deprivation therapy as metastatic hormone-naïve prostate cancer in 14 hospitals between September 2008 and October 2018. Overall survival (OS) and OS after castration resistance (OS-CR) were compared between the <12 months (TCR <12M) and ≥12 months (TCR ≥12M). The association between the first-line life-prolonging therapy (docetaxel or new androgen receptor-targeted agents: ART) and TCR on OS-CR was investigated using multivariate Cox regression analysis via inverse probability of treatment weighting (IPTW) model. Results: Median age and time to CRPC were 72 years and 12 months, respectively. The number of patients in the TCR<12M and ≥12M groups were 137 and 146, respectively. Of 283, baseline parameters such as age, extent of disease (EOD), hemoglobin (Hgb), lactate dehydrogenase (LDH), and serum albumin levels were significantly differences in between the groups. We observed significantly poor OS and OS-CR in the TCR <12M group than those in the TCR ≥12M group. First-line docetaxel therapy did not significantly improved OS-CR regardless of TCR. Background (age, ECOG PS, GS, Hgb, tumor volume, serum data, and TCR)-adjusted multivariate Cox regression analyses showed that first-line docetaxel therapy was significantly associated with shorter OS-CR than first-line ART therapy in the TCR <12M group. Conclusions: The prognostic impact of TCR on OS was significant. However, the association between the first-line life-prolonging therapy and TCR on OS need further study.