Objective To investigate the predictive value of spiral CT in composition changes of pediatric urinary.Methods A total of 25 pediatric patients with urinary stones were investigated.Eighteen patients with renal stones were stratified into two groups:an alkalization therapy alone group ( n =9 ) and a comprehensive therapy group (n =9).Flame atomic absorption spectrum (AAS) was employed to measure calcium level of the pediatric urinary stones.Spiral CT was employed to measure the peak CT number in vitro of all the pediatric urinary stones and 61 adult urinary stones,which served as controls.Results All pediatric urinary stones contained calcium ( 0.11％ - 26.30％ ).A positive correlation was observed between the CT number of pediatric urinary stone and its stone calcium level ( r =0.855,P ＜ 0.01 ).Compared to the alkalization therapy alone group,the CT number and stone calcium level of pediatricrenal stones in the comprehensive therapy group were significant higher (stone CT number:162 ± 60 HU VS.783 ±476 HU,P ＜ 0.01 ; stone calcium level:1.30 ± 1.52％ VS 19.83 ± 7.48％,P ＜ 0.01 ).Compared to ≤400 HU pediatric renal stones,＞ 400 HU renal stones contained more calcium (21.71 ± 5.27％,1.65 ±1.82％,P ＜ 0.01 ) and failed to dissolve by alkalization therapy alone ( x2 =11.455,P ＜ 0.01 ).Conclusions CT could be a predictive tool for composition changes of pediatric urinary stones.In clinical CT scanning setting,＞400 HU pediatric urinary stones probably will contain more calcium and not be suitable for alkalization therapy alone.