Abstract: In order to understand the molecular basis of chicken heterosis, mRNA differential display method was used to analyze the differential gene expression of ovary tissue between hybrids and their parental lines in a 3×3 diallel cross involving 3 chicken breeds, which were White Plymouth Rock（EE）, CAU Brown（DD）and White Leghorn(AA). Only bands that can be repeated in duplicate DDRT-PCR amplification were used for statistic analysis. Our results showed that differences of gene expression between hybrids and their parent lines were very obvious both in quantitative and qualitative. By using 24 pairs of primer combination, a total of 1 572 bands were displayed, and 71.63% (1 126 out of 1 572) can be repeated. The average differential expression band of 6 hybrids is 169.67(15.07%), which were grouped into seven types of differential expression patterns: Over-expression of parental fragements in hybrids (P1=22.29%)，hybridspecific expressed fragements (P2=9.84%)，Under-expression of parental fragements in hybrids (P3=9.85%)，hybridabsence expressed fragements (P4=3.42%)，parent-specific expressed fragements (P5=22.91%)，Dominant expression fragements of single parent in hybrids (P6=25.74%)， Co-dominance expressed fragements (P7=5.95%). Correlation analysis indicated that there are significant negative correlation or significant correlation between the pattern of P2 or the pattern of P3 and heterosis percentage of 32 week-old egg number, which indicates that hybrid-specific expressed fragements or Under-expression of parental fragements in hybrids are likely to restain or strengthen the heterosis forming of 32 week-old egg number.