肾小球（英语：Glomerulus、肾丝球）是肾元中的用于将血液过滤生成原尿的一团毛细血丛，被鲍氏囊（英语：Bowman's capsule）所包裹，是尿液形成的重要构造。

血液经由入球小动脉进入肾小球。肾小球内的微血管不像其他微血管，汇流入静脉，而是流入出球小动脉。在肾小球内，微血管受到高压，而加速了超滤作用（ultrafiltration）的进行。微血管中的血液经由超滤作用之后，形成滤液，渗入鲍氏囊内。

肾小球与鲍氏囊合称为肾小体，肾小球的过滤速率便称为肾小球过滤率（glomerular filtration rate，GFR/肾丝球过滤率）

A glomerulus is a network (as a tuft) of capillaries located at the beginning of a nephron in the kidney. It serves as the first stage in the filtering process of the blood carried out by the nephron in its formation of urine.

The glomerulus is surrounded by a cup-like sac known as Bowman's capsule. The blood plasma is filtered through the capillaries of the glomerulus into the capsule. The Bowman's capsule empties the filtrate into the proximal tubule that is also part of the duct system of the nephron.