The 29-year-old actress and 42-year-old actor were all smiles when they were spotted holding hands in Hawaii.
The estranged couple stayed at the Four Seasons Hualalai, where they wed in 2010.
Fox and Green's vacation follows word that the actress is pregnant with their third child.
She and Green, who confirmed he's the father, already share 3-year-old Noah and 2-year-old Bodhi and brought the boys along on the trip.
"They are doing great and had the best vacation with the kids," a source told People magazine. "They have so many happy memories from Hawaii and wanted to relax for a few days together."
Fox and Green met on the set of "Hope & Faith" in 2004 and announced their separation in August. The actress filed to end their marriage shortly after the announcement, but many now expect the pair to call off their divorce.
"Brian and Megan are officially back together," an insider told E! News. "They want to be a family. Divorce is not happening at all. They have worked through some issues and are more in love than ever now."
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"He is a good guy," the source added of Green. "The attraction is really strong still. Both families are really happy they have worked it out and are going to stick together. This baby on the way has brought them even closer."
Fox will next reprise the role of April O'Neill in "Teenage Mutant Ninja Turtles: Out of the Shadows" and is also slated for "Zeroville" with James Franco.
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