R&D Div. #3 (第三研究開発本部 開発一部) was the first third division of Sega Interactive. It was spun out of Sega R&D1. It is unclear exactly when it was founded, but it seems to have coincided with the founding of Sega Interactive. The earliest recorded public mention of its existence came in November 2015, and in December the company's recruitment page was updated to mention R&D3 for relevant products instead of R&D1.

R&D3 acted as a spiritual successor to Sega AM3, which had merged with AM1 in 2008. However, it was not a direct replica, as various former AM3 staff remained at R&D1, as did their former franchise Initial D Arcade Stage (although there is very little public evidence to confirm or deny this). Instead, it carried over former AM3 franchise World Club Champion Football, and R&D1’s new franchises maimai and Wonderland Wars.

R&D3 was best known for its trio of rhythm game series: the afore-mentioned maimai, Chunithm (conceived at R&D1) and the brand new Ongeki. This naturally led to the department's sound section being the best-known for all R&D departments, especially as one of its members was Takenobu Mitsuyoshi. R&D3 overall mostly maintained and updated existing series, with Ongeki and the retooled WCCF Footista being the closest the department had to brand new games.

It was merged with Sega Games in 2020, becoming a new department in the 5th Development Div. of Sega Asia & Japan Studio HQ.