Off-duty police sergeant Julian Williams and friends Mark Gohegan and Francis Godwin were on the beach when they heard screaming and saw somebody waving for help.
They jumped on their windsurf boards and made their way to the duo 150 metres off the beach.
Julian said, "There were two young men who had been out on a kayak which had capsized. One of them was going under the water against the tide and the other lad was just about managing to tread water.
"I dragged one on to my board and Mark and Francis reached the other and put him on his board and we managed to swim back to shore with them."
Julian, who is based at Hammonds Drive police station in Eastbourne, said the two men were in grave danger.
"Without a doubt they would have died had we not got to them," he said.
The RNLI's inshore lifeboat was also called out to help with the rescue shortly after 3pm. The lifeboat's deputy medical adviser and crew member Dr Stephen Lytton was taken ashore to check on the casualties for any injuries.
An ambulance was called and the two men taken to hospital while the crew on the inshore lifeboat recovered the upturned kayak and towed it ashore.
The two men, believed to be in their early 20s, were dressed in t-shirts and shorts and are believed to have been drinking.
The incident has prompted warnings from Dover coastguard to people to take care when they go out on the water.
Gordon Wise, the watch manager at Dover Coastguard said, "People should always wear a lifejacket in a kayak because of the sheer danger they might face if it tips over.
"People should also remember the sea temperature is still very cold and won't be any warmer for another two or three months. People are on the beach and their bodies are warm but they plunge into the cold water and it can be very dangerous and even spark a heart attack.
"Alcohol will also reduce people's tolerance to the cold water and the advice is if you have been drinking, stay on the beach and don't venture into the water. It's not a good idea."