Local newspaper Heraldo said Agustin Aliaga and his wife Juani Sanchez had lost the ring in 1979, just five months after they were married, while swimming near the Spanish resort of Benidorm.
The couple believed the ring to be lost forever until a diver found it in August.
Jessica Nisos posted a photo of the ring hoping to find its owners.
She wrote: "I found a wedding ring diving off the island of Benidorm. I wish I could give it back to the owner. It has been lost for a long, long time because it was covered in sediment.
"It is from a couple who got married on 17-02-1979. Could you share this please? It's important to me to return it. Many thanks to all. Please share this."
As requested, more than 80,000 people shared the post on Facebook.
Mr Aliaga's niece, who lives in the Benidorm area, saw the post and put her aunt and uncle in contact with Ms Nisos.
Having sorted through 300 messages she had received, Ms Nisos was finally able to return the ring to the Aliagas.
Mr Aliaga said: "So that she could see it was totally true, we send a photocopy of our family register and a picture of the wedding ring.
"When my wife told Jessica her name, Jessica began shouting with excitement.
"It was a pleasant surprise, because more than the material, the important thing is symbolic and emotional, as it is the ring that we were married with in the church."
A Spanish couple have been reunited with a wedding ring they lost 37 years ago.