A frame structure for a foldable chair comprises a front interconnecting supporting unit, a rear interconnecting supporting unit, a lateral interconnecting supporting unit, an armrest unit, a seat supporting unit, an armrest unit, and a transverse supporting rod. The front interconnecting supporting unit is installed with a front leg unit, a crisscrossed supporting unit. The rear interconnecting supporting unit comprises a rear leg unit, an arc-shaped supporting unit of which one end of each section is curved in shape. Each of the lateral interconnecting supporting unit includes two board members pivotally crisscrossed connected with each other between the front and rear leg unit. Beneath the armrest unit, a gliding rod is extending along thereof and a connecting joint is protruding there from. The transverse supporting rod is formed with a connecting plate, a rod and a connecting joint.