The present invention is a chain structure of bicycles, which comprises a plurality of rollers, a plurality of chain sheets and a plurality of chain rollers. Wherein the rollers define a mounting space. Each chain sheet comprises a chain body, a first pivot joint part extending from one end of chain body and to be arranged in the mounting space, a second pivot joint part horizontally extending from the other end of chain body, the second pivot joint part is installed on the roller with the first pivot joint part, wherein the first pivot joint part is in a horizontal position different from chain body, the first pivot joint part defines a rotation space for placing the second pivot joint part of another chain sheet, so that the first pivot joint part and second pivot joint part can rotate a preset angle in the rotation space. When the chain sheets are combined with rollers respectively, the chain bodies remain on the same plane, the chain roller penetrates the second pivot joint part and the first pivot joint part respectively for connecting the roller to the chain sheets on both sides of roller. Thereby, the chain is thinned and the weight is reduced, the tensile strength is increased by thickening the chain sheet.