The urine osmolality test is one of the urine tests. The level of osmolality is mainly related to the number of particles in the solution that cannot pass through the semi-permeable membrane. Urine is not pure water, which contains a large number of particles involved in the formation of osmolality. When kidney function is impaired, the type and number of particles excreted into the urine will also change, and the urine osmolality will change accordingly, therefore, urine osmolality examination has an auxiliary diagnostic role in kidney diseases. Normal urine osmolality is generally between 700 and 1000 mOsm/(kgH2O), with morning urine having a slightly higher osmolality. Increased urine osmolality can be seen in diarrhea, dehydration, cardiac insufficiency and acute nephritis. Decreased osmolality can be seen in uremia, chronic renal failure, polycystic kidney and chronic pyelonephritis. It is recommended to go to the hospital for further counseling.