A process for producing a high-molecular-weight polydioxolane, which includes the steps of: polymerizing 1,3-dioxolane using a polymerization catalyst comprising a heteropolyacid and a ketone; and neutralizing the resulting polymerization reaction product using an organic amine and/or ammonia. A hydrophilic film, which includes a resin including a polydioxolane and having a particular molecular weight and has a particular crystallinity and a particular spherulite's size. A film crumbly in cold water is produced by forming a film under particular forming conditions from a resin including a polydioxolane and having a particular molecular weight, or by subjecting an already formed film to particular thermal hysteresis.