The actress was spotted relaxing in a bikini with Law and his three children on one of the Caribbean island's white sand beaches on Sunday (27Dec09). They were also photographed giggling with delight during a dinghy ride.
Miller is said to have spent Christmas Day (25Dec09) in Barbados, while the actor and his sons Rafferty, 12, and Rudy, seven, and daughter Iris, nine, flew in on the 26 December (09) after spending time with their actress mother Sadie Frost in London.
The couple has reportedly checked into a beachfront villa, where they will celebrate Miller's 28th birthday on Monday (28Dec09) and Law's 37th on Tuesday (29Dec09).
It is the first time the Alfie co-stars have been photographed together since they split in 2006 after Law's fling with his children's nanny was exposed in the press.
Despite almost four years apart, both stars have struggled to find lasting love - Miller ended her on/off relationship with actor Rhys Ifans, and endured a romance with married actor Balthazar Getty earlier this year (09), while single Law became a dad for the fourth time in September (09) following a brief fling with American model Samantha Burke.