The aim of this chapter is to focus on the urinary urea estimation. Urinary urea can be estimated as blood urea but the urine must be diluted 1–10 times or up to 20 times with distilled water. Total daily excretion of urea in urine is 20 g and average concentration being 20 g/L on an ordinary diet. The excretion varies with dietary intake of protein. Urine urea over successive 24 hours periods is helpful in the management of acute renal failure cases. This chapter covers the urea clearance, method of estimation, interpretation, and grading of renal function on the basis of urea clearance.