The aim of the present study was to investigate the prognostic factors for patients with primary unresectable renal cell carcinoma (RCC) with synchronous distant metastasis receiving molecularly targeted therapies. A total of 26 patients with primary unresectable RCC with synchronous distant metastasis underwent molecularly targeted therapies at the Kurume University Hospital (Kurume, Japan) between March 2008 and March 2016. Early primary renal tumor response was evaluated at 8-12 weeks after the introduction of molecularly targeted therapy and a 10% decrease in the diameter of primary renal tumor was used as the cut-off value. The median overall survival from the initiation of first-line molecularly targeted therapy was 18.3 months. Univariate analyses for various factors identified early primary renal tumor response (P=0.0004) and best response to first-line treatment (P=0.0002) as prognostic variables. Multivariate analyses also identified early primary renal tumor response (P=0.0099) and best response to first-line treatment (P=0.0054) as independent prognostic factors. A comparison of clinical characteristics between the group with ≥10% shrinkage and the group with disease progression or <10% shrinkage revealed that the number of metastatic sites and pretreatment monocyte-to-lymphocyte ratio tended to be predictive factors for primary renal tumor response. These results suggest that early primary renal tumor shrinkage is highly variable for patients with primary unresectable RCC with synchronous distant metastasis receiving molecularly targeted therapies.