Abstract: Using suppression subtractive hybridization (SSH),two subtracted cDNA libraries were constructed for mitten hand crab (Eriocheir japonica sinensis) ovaries in two periods of developments.Two-directional (forward and backward) SSH was performed on cDNAs of mitten hand crab ovaries in periods Ⅱ or Ⅲ.Two-directional subtracted cDNA fragments were cloned into PinPoint plasmid vectors,and the vectors were transformed into E.coli JM109.Finally,the forward and backward subtracted cDNA libraries (863 and 360 clones,respectively) were obtained.By PCR detection,the length of the inserted fragments of the forward and backward subtracted cDNA libraries was 360 and 160 base pairs on average,respectively.The results showed that the subtracted libraries constructed were suitable for further study on the genes related to the development of the mitten hand crab ovary.