The present invention relates to a lactide copolymer exhibiting excellent flexibility and having more improved processability and productivity at the time of performing an extrusion and molding process, and a resin composition and film including the same, wherein the lactide copolymer includes a predetermined number of block copolymer repeating units in which hard segments of polylactide repeating units are bound to both ends of soft segments of polyether polyol repeating units, and has a weight-average molecular weight of 150,000 to 300,000, and a melt index y (MI; g/10 min) satisfying a specific relationship, the MI being measured under a load of 2.16 kg and at a temperature of x□ between 170□ and 210□.