A mechanism for a seat portion of a baby carriage, the seat portion including a seat floor and a back rest disposed at a rear portion of the seat floor, the mechanism including a pair of operating links, each having a central portion which is swingably pivoted to a lower end of a central portion disposed inside of the back rest; engaging rods pivoted to ends of the operating links such that the engaging rods swing in a horizontal direction in accordance with a swinging operation of the operating links; a pair of receiving plates respectively disposed on both ends of the seat floor, each of the receiving plates having several spaced fitting holes for selectively receiving ends of the engaging rods so as to provide a reclining operation of the seat portion; and a swing operating plate attached to a lower end portion of the back rest so as to be freely lifted, upper ends of the two operating links being pivoted to the swing operating plate.