A ball sealer for hydrocarbon resource collection is provided, wherein the ball sealer is obtained from a roughly spherical structure overall that has at least a two layer structure of a spherical core and a surface layer resin material covering same; at least the surface layer resin material thereof is obtained from a polyglycolic acid resin; and the diameter is about 25 mm (1 inch) or more. The ball sealer is manufactured by a method, wherein the spherical core is disposed substantially in the center of a metal mold cavity with support pins; in this state, the surface layer resin obtained from the polyglycolic acid resin is injection-molded around the core; and after retracting the support pins to the wall surface of the metal mold cavity synchronized with completion of the injection of the surface layer resin, the surface layer resin is cured. A large diameter ball sealer is thereby manufactured with a relatively simple process and with good dimensional accuracy, the ball sealer being suitable for use in hydraulic fracturing, which is widely used for collecting hydrocarbon resources such as petroleum and natural gas, and having a polyglycolic acid resin, which is a biodegradable resin with good mechanical strength and good dimensional designability, for at least the surface layer-configuring resin.