Objective To determine the bone mineral density of tibia in healthy children aged 3~6 years old in Zibo area and set up normal reference value of speed of sound(SOS) for preschool children. Methods 7 920 children aged 3~6 years old,who hand body examination in kindergarten were selected and according to the age divided into 12 groups ( every 3 months apart as a group).Their tibias SOS were assayed by adopting quantitative ultrasound system.Height and weight of subjects were measured, and body mass indexes were calculated.The data were analyzed by using SPSS 20.0 software. Results With the age increasing,the values of tibias SOS increased in general more over,SOS was closely related positively to age(r=0.209,P＜0.01).There were significant differences of SOS between boys and girls aged 3~6 years old within the same age group (P＜0.05).There were significant differences of SOS between healthy children and obese children aged 3~6 years old within the same age group (P＜0.05). Conclusions SOS of tibias are related to age.SOS of tibias are different between male and female in preschool children,and SOS of tibias of obese children are lower than the other children.The reference value of SOS should be set up according to the age and sex.