Disclosed are a lactone-modified polyvinyl alcohol and a process for the preparation thereof, a polymer composition, a permanently anti-electrostatic resin composition, a lactone-modified resin having hydroxyl groups, and a process for the preparation thereof. The lactone-modified polyvinyl alcohol can be used in wide fields owing to the capability of freely adjusting the water solubility, such as water-soluble, gradually water-soluble, low water-soluble, and water-insoluble by a degree modified by lactone compounds, and owing to possessing properties both of PVA and lactones. Furthermore, the lactone-modified polyvinyl alcohol has properties such as being plasticizers or softening agents, and as a result, there can be provided a polymer composition having excellent properties by mixing with a hydrophilic polymer or polar polymer. Still further, a blend resin composition in which a variety of resins are blended with the lactone-modified polyvinyl alcohol has an excellent permanently-anti-electrostatic property, and the resin composition having a permanently-anti-electrostatic property can be preferably employed as a variety of molded articles such as parts for electric appliances, textiles, films, etc.