A resin composition for producing a film or sheet having high tear strength that is excellent in processability, mechanical properties, and biodegradability. The resin composition is a biodegradable polyester resin composition containing: (i) an aliphatic polyester (P3HA) having a repeating unit of formula (1): [—CHR—CH2—CO—O—] (1), wherein R is an alkyl group represented by CnH2n+1, where n is an integer of 1 or more and 15 or less; (ii) polybutylene adipate terephthalate (PBAT); and hydrophilic silica (A), wherein a weight ratio of the aliphatic polyester (P3HA) to the polybutylene adipate terephthalate (PBAT) is 90/10 to 10/90, and an amount of the hydrophilic silica (A) is 2 to 30 parts by weight with respect to 100 parts by weight of a total amount of the aliphatic polyester (P3HA) and the polybutylene adipate terephthalate (PBAT) combined.