The invention discloses a seat structure of a foldable baby stroller. The seat structure of the foldable baby stroller comprises backrest tubes, side handrail frames, leg rest tubes and a front handrail, wherein the backrest tubes, the side handrail frames and the leg rest tubes are symmetrically arranged at the two sides. The lower end of each backrest tube and the upper end of each leg rest tube are respectively connected with one side handrail frame in a rotary mode. The two ends of the front handrail are fixed to the portions above the two side handrail frames. The seat structure of the foldable baby stroller is characterized in that the inner sides of the two side handrail frames are respectively provided with a side seat board in a rotary mode, a middle seat board is arranged between the two side seat boards, the middle seat board is connected with the two side seat boards in a rotary mode, the seat structure of the foldable baby stroller is divided into the seat boards connected in the rotary mode, so that when the baby stroller is folded, the middle seat board located in the middle position is lifted, the ends, connected with the middle seat board, of the side seat boards arranged at the two sides rotate upwards as well, the folding amplitude is large, and the baby stroller is folded completely. The seat structure of the foldable baby stroller is simple, convenient to operate and capable of enabling the assembly process to be simplified, improving the production efficiency and guaranteeing the use convenience and the safety of a seat.