The modulus of elasticity between the perovskite and rock salt blocks (the unit cell of YBa 2 Cu 3 O 7 - δ is composed of them) in Y-system superconductors (YBa 2 Cu 3 O 7 - δ , δ=0.07-0.62) have been calculated. A clear correlation among the superconducting transition temperature and the modulus of elasticity between the perovskite and rock salt blocks in the Y-system superconductors is established. Also, the correlation between the static mechanical properties and the superconducting transition temperature was discussed. We suggest that the perovskite and rock salt blocks are somewhat independent structural units in physical properties, and the interaction between the two blocks is important in determining the superconducting properties.