The effect of cAMP levels on the fluidity of human erythrocytes membrane phospholipid is studied. When the cAMP levels are low, cAMP produces phospholipid molecules less ordered. When the cAMP levels are high, it has the opposite function for the above mentioned part of phospholipid. Generally, cAMP causes the long nonpolar chains in higher gauche configuration fraction. The effects of cAMP levels on the packing of the long nonpolar chain are not very notable. cGMP has the negative function on the membrane phospholipid. ATP has no notable effect on the membrane phospholipid. But cGMP or ATP weakens the function of cAMP and even causes the mixture of cAMP-cGMP or cAMP-ATP having an opposite effect compared to that of pure cAMP.