There is provided a P3HA resin composition to which a crystal nucleating agent suitable for the promotion of the crystallization of a P3HA resin is added. A poly(3-hydroxyalkanoate) resin composition comprising: a poly(3-hydroxyalkanoate) resin; and a metal salt of a phenylphosphonic acid compound of Formula [1]: (where R1 and R2 are each independently a hydrogen atom, a C1-10 alkyl group, or a C2-11 alkoxycarbonyl group), wherein the metal salt is at least one selected from the group consisting of a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a calcium salt, a barium salt, a manganese salt, an iron salt, a cobalt salt, a nickel salt, a copper salt, a silver salt, an aluminum salt, and a tin salt.