A polyester resin composition including a ketene imine compound represented by the Formula (1) and polyester shows excellent hydrolysis resistance and prevents yellowing. At least one of R11, R12, R21 and R22 represents an alkyl, aryl, alkoxy or aryloxy group which may have a substituent; R15 and R25 represent an alkyl, aryl, alkoxy or aryloxy group which may have a substituent; R3 represents an alkyl or aryl group which may have a substituent; and a and b represent an integer of 0 to 3.