Solubilities of argon, oxygen and nitrogen were determined in 1,2-propanediol+water mixed solvent over the full range of composition by a static method. Gas solubility measurements were carried out at a temperature of 298.15 K and pressure of 10133 kPa. Both the excess quantity referring to the Ostwald coefficient and to the excess volume of solvent mixture showed similar relation having minima against the volume fraction composition of 1,2-propanediol. The order of gas solubility expressed by the Ostwald coefficient in 1,2-propanediol+water mixed solvent was argon > oxygen > nitrogen in full range of composition. Furthermore, the excess Ostwald coefficients on the basis of volume fraction which express the non-ideality of gas solubility in non-ideal solutions were defined, and excess Ostwald coefficient of these three solute gases in 1.2-propanediol+water mixed solvent showed one parabolic curve against volume fraction of 1,2-propanediol. This result means that excess Ostwald coefficients of these gases do not depend on the type of solute gas, but on solvent. This property was similar to that of monoalcohol aqueous solutions.