The density of glycine, L-alanine, and L-serine in formamide-water mixtures was measured at 298.15 K and used to calculate the apparent molar volume V-phi, and limiting partial molar volume V-phi degrees of the amino acids. Transfer partial molar volume Delta V-tr(phi)degrees from water to formamide-water mixtures and the volumetric interaction coefficients were also obtained to interpret the solute-solvent interaction. Values of Delta V-tr(phi)degrees of the three amino acids were all positive and increased with increasing formamide concentration in the mixtures, in the order of L-alanine < glycine < L-serine, which was consistent with the cosphere overlap model. The interaction of formamide molecules decreased its structural-breaking effect and consequent interaction with amino acids, leading to negative triplet interaction coefficients.