A golf bag cart foldable device includes a bottom cart stand having a rear wheel frame at each side to link a rear wheel. The bottom cart stand has a bag base to link a front wheel. An upper cart stand is in pinned connection with the bottom cart stand. A linkage set, including plural linkages, forms links between the upper cart stand and the bottom cart stand and between the upper cart stand and the rear wheel frame. A folding joint enables release of the folding joint first. By the link between the linkage set and the rear wheel frame, simultaneous unfolding or folding of the upper cart stand, the bottom cart stand and the rear wheels can thus be accomplished. The folding joint is secured to have the upper cart stand and the bottom cart stand locked to each other, to achieve handiness in use.