Regulus III was the third planet of the Regulan planetary system. This system was located in the Alpha Quadrant. It was located three hundred light years from Deep Space 9. This was one of two planets that supported life in this system; the other was Regulus V.
In 2371, Jake Sisko's girlfriend, Mardah, was accepted to the Science Academy on this world. Benjamin Sisko was proud of her, stating that it was a good school. (TOS: "Amok Time"; Star Trek VI: The Undiscovered Country, production art; DS9: "Fascination")