Objective：To investigate microRNA(miRNA)expression profile of placental tissues between gestational diabetes mellitus (GDM)and normal pregnant women．Methods：A total of 20 cases of pregnant women with GDM were randomly selected from Armed Police Hospital Affiliated to Guangzhou Medical College and Zhujiang Hospital of Southern Medical University in January 2013 to January 2014，and notmal pregnant Han women from Guangdong without complications in the same period were enrolled as control．Placenta was obtained after delivery tollowed by total RNA extraction with Trizol．Five samples of total RNA were randomly picked and mixed as the GDM and notmal control group，respectively，for next step．miRNA library of GDM and control was built by the reverse transcription method and used for investigation of expression of various miRNAs by high throughput sequencing．Results：Purified total RNA was extracted from placenta and miRNA library was successfull constructed．After transition from raw data，there were over 10 000 000 clean reads with 21-24 nt-long small RNA the most among which miRNAs were over 30％ in each group．After removal of other RNA by comparison between Rfam and Genebank database over 7 000 miRNA species were accounted for．A total of