An association equation of state (AEOS) has been proposed for,for hydrogen-bonded compounds. To obtain this AEOS, the compressibility factor was assumed to consist of two parts: the physical part due to physical interactions of molecules; and the chemical part due to molecular association by hydrogen bonding of molecules. The physical part of the compressibility factor was represented by the MMM EOS for non-polar compounds proposed by Mohsen-Nia et al., Fluid Phase Equilib. 206, 27-39 (2003), and the chemical part of the compressibility factor was deduced by proposing a molecular association model of infinite series.