A folding joint of a golf bag cart includes a main body fixed onto a cart frame and having a chamber formed inside the main body and a long slot formed on both sides of the chamber separately. A driving block is installed in the chamber of the main body. A spring installed at an upper end of the driving block, and a latch rod is disposed on both sides of the driving block separately. Two rotating members, each has an upper end coupled to the cart frame, a lower end coupled to the main body, and a slide slot with a latch slot formed on the slide slot. Thus, the folding joint can be folded or unfolded to secure the cart frame automatically, to provide a simple and convenient operation.