Fruit softening is mainly caused by the cell wall modifications. Mannan is one of cell wall components, and its complete breakdown requires endo-β-mannanase (EC 3.2.1.78, β-Man). In the present study, the expression pattern of β-Man activities and genes in fruits, as well as the changes of fruit firmness and ethylene production were monitored during peach fruit storage. The results showed that the β-Man activity in both skin and mesocarp increased concomitantly with the loss of firmness and ethylene release during peach fruit storage. In addition, β-Man activity in skin was significantly higher than that in mesocarp. Two partial cDNAs of PpMAN1and PpMAN2 were obtained from mature peach fruit. The accumulation of PpMAN1 and PpMAN2 in both tissues exhibited a steady decline with the peach fruit softening during storage, which positively correlated with the loss of fruit firmness, but negatively correlated with the increase of β-Man activity and ethylene production.