Objective To identify the prevalence of asymptomatic hematuria between 3 to 6 years old children of Luogang district,Guangzhou city. Methods Totally 5 602 children between 3 to 6 years in Luogang District were included in our study.Each child was received routine urinalysis.Asymptomatic hematuria was diagnosed as three consecutive times of microscopic hematuria in two weeks.The children with asymptomatic hematuria were received more tests in order to find out the causes of the disease. Results The incidence of asymptomatic hematuria in Luogang District was 0.88%(49/5 602).The incidence was different between boys and girls(0.64% vs 1.14%,P<0.05).Forty children with asymptomatic hematuria were received further examinations.As a result,left renal vein entrapment syndrome was the most common cause (n=9,22.5%).Idiopathic hypercalciuria (n=5,12.5%),urinary tract infection (n=5,12.5%) and acute glomerulonephritis (n=3,7.5%) were also common.There was only one child with purpura nephritis,IgA nephropathy,polycystic kidney disease or hydronephrosis respectively.Unfortunately,the causes of the last forteen children (n=14,35%) with asymptomatic hematuria were still unknown.Conclusions The incidence of asymptomatic hematuria in children between 3 to 6 years was 0.88%.The common causes of the disease are organic diseases which might lead to long-term kidney injury in the future,so we should try to diagnose and treat as early as possible.In a conclusion,we suggested that routine urinalysis should be included in children's health care programme.