Abstract: For understanding the gene expression information in roots of trifoliate orange（Poncirus trifoliata），an excellent citrus rootstock，a full-length cDNA library was successfully constructed with the root material. According to the quality analysis results，the library reached 1.08 × 106 cfu ? mL-1 in capacity with a recombinant efficiency as high as 95%. One hundred and eighty-two expressed sequence tags（ESTs，GenBank No.：JK316116–JK316297）were obtained from 200 clones that were randomly selected from the library，and then subjected to further assay. Among 96 unigenes obtained from those ESTs，which included 12 contigs and 84 singletons，68 unigenes were homologous with the genes in GenBank database while 56 unigenes were homologous with the citrus genes published. These unigenes may have biology function such as binding，catalytic activity and so on，and may play important roles in biology process such as cellular process，metabolic process，response to stimulus and so forth. Twenty-four unigenes were annotated among the 36 genes with the open reading frame（ORF）and 9 genes might be related with stress responsing or root developing.

Key words: Poncirus trifoliata, root, full-length cDNA library, expressed sequence tages, bioinformatic analysis