Objective: To analyze the clinical and pathological features of small renal cell carcinoma (RCC), especially of those with diameter less than 4 cm and to understand the characteristics and factors related to recurrence and progression.Methods: A total of 200 patients with RCC were stratifiedly selected for retrospective analysis. Their baseline demographic features, tumor-specific clinical features, pathological features of renal lesions, especially microscopic features were collected. The patients were divided according to the largest diameter of renal tumor lesions. Univariate analysis was used to compare the differences between tumor staging and microscopic pathological features between the groups. Binary multivariate Logistic regression was used to investigate factors related to tumor progression and prognosis in the patients with small RCC.Results: The tumor diameters of 127 RCC patients were less than 4 cm and most of them had clear cell renal cell carcinoma (ccRCC). The increase in tumor diameter resulted in significantly higher T stage (P<0.01), higher WHO/International Society of Urological Pathology (ISUP) grade (P<0.05) and increasing chance of lymph node metastasis (P<0.01). Even when the tumor diameter was less than 4 cm, the patients might still have perirenal fat invasion, renal sinus invasion and greater elevated tumor grade (greater than grade 3) and synchronous lung metastasis. The incidences of intravascular thrombus (9.3% vs. 0) and tumor necrosis (27.8% vs. 5.5%) in the patients with RCC between 4-7 cm were significantly higher than those with RCC less than 4 cm (P<0.01). Sub-group analysis of small RCC (less than 4 cm) indicated that the patients with RCC between 2-4 cm were more likely to have intratumoral hemorrhage (44.7% vs. 23%, P<0.05) and necrosis than those with RCC less than 2 cm (8.2% vs. 0, P=0.095). Logistic regression analysis of small RCC showed that the incidence of tumor invasion to renal capsule was higher in ccRCC (OR=5.15, 95%CI: 1.36-19.52). Necrosis was closely related to the formation of peritumor pseudocapsule in small RCC (OR=14.90, 95%CI: 1.41-157.50). Increase in the tumor diameter was related to higher tumor grade (greater than grade 3) (OR=3.49, 95%CI: 1.11-10.93).Conclusion: The tumor stage and grade of small RCC (less than 4 cm) are low, but extra-renal invasion and synchronous distant metastasis may occur. Internal hemorrhage and necrosis in tumor, ccRCC subtype, along with microscopic features, such as the renal capsule invasion and perirenal pseudocapsule formation are relevant factors of malignant behavior of small RCC and could be considered in prognosis evaluation.