【Objective】 To investigate the relationship between initial serum testosterone level and aggressive characteristics, progression and prognosis of metastatic prostate cancer (mPCa). 【Methods】 The clinical data of 302 mPCa patients diagnosed with biopsy and auxiliary examinations at the First Affiliated Hospital of Xinjiang Medical University during Aug. 2010 and Aug. 2022 were retrospectively analyzed, including 148 cases in the serum testosterone low level group (≤12 nmol/L) and 154 in the normal level group (>12 nmol/L). The independent risk factors associated with aggressive features were analyzed with multifactorial logistic regression, survival was determined with Kaplan-Meier method, the independent risk factors affecting progression and prognosis were identified with multifactorial Cox regression modeling, and the value of initial serum testosterone level in predicting the progression and survival was assessed with receiver operating characteristic (ROC) curve. 【Results】 The low level group had a higher proportion of Gleason score ≥8, T stage >3, initial prostate-specific antigen (PSA) >200 ng/mL, high tumor load, visceral metastasis, PSA≥0.2 ng/mL after 6 months of treatment, and higher body mass index (BMI), but the PSA decline rate after 6 months of treatment was lower than that in the normal level group (P<0.05). Multifactorial logistic regression showed that initial serum testosterone level >12 nmol/L was a protective factor for high tumor load (OR=0.137, 95%CI:0.070-0.265, P<0.001), Gleason score ≥8 (OR=0.371, 95%CI:0.184-0.750, P=0.006) and visceral metastasis (OR=0.337, 95%CI:0.175-0.652, P=0.001). The median progression-free survival was shorter in the low level group than in the normal level group (15 months vs. 20 months, P<0.001), and the median overall survival time was also shorter (45 months vs. 86 months, P<0.001). Multifactorial Cox regression analysis showed that Gleason score ≥8, high tumor load, PSA value at 6 months of treatment, and PSA decline rate were independent influencing factors for progression to castration resistant prostate cancer (CRPC) (P<0.05).The risk of death in patients with high tumor load was 2.510 times higher than that of patients with low tumor load (95%CI:1.555-4.051, P<0.001). ROC curves showed that initial serum testosterone level could predict the risk of progression to CRPC (AUC:0.645) and survival (AUC:0.595). 【Conclusion】 Low level initial serum testosterone is associated with an aggressive profile and poor prognosis of mPCa, and can predict the risk of progression and survival status of mPCa patients.