Abstract: A deck umbrella support system securely retains an umbrella attached to an umbrella pole on a deck, wherein the deck has a receiving aperture formed through a surface thereof. The deck umbrella support system may include a mount assembly having a mount tube with a mount plate attached to it. The mount tube has an upper end and a lower end, wherein the upper end includes a mount aperture formed through it. An adapter assembly, which is at least partially hollow, includes an adapter tube which is designed and configured to receive at least a portion of the umbrella pole therein and to be inserted into the mount tube via the mount aperture. A locking assembly is disposed proximate to the lower end of the mount tube to secure the adapter tube in the mount tube.