RNAs of the leaves in Avicennia marina, which cultured in 50@1000 and 0@1000 salinity condition respectively, were isolated for mRNA differential display analysis. Screened by OligodT12 GC and eight 10-oligonucleotide arbitrary primers, differential cDNA fragments-csrg1(600 bp), csrg2(550 bp), csrg3(480 bp), only appeared in the leaves of Avicennia marina cultured in 50@1000 salinity condition. After detected by RNA dot hybridization, only csrg1 appeared the difference between the RNAs of the leaves in Avicennia marina cultured in 50@1000 and 0@1000 salinity condition respectively, and csrg1 was confirmed as the salt-tolerant cDNA. csrg1 was cloned and sequenced. After searching in Genbank, there were no similar sequences reported.