Hookers Ricky Jackson and Henry Bell have been locked in, as have utility back Josh Timu and lock Josh Hill.
All have re-signed for two-year deals except Jackson, who has signed for a single year.
It gives the squad an increasingly complete look and adds quality in several areas.
The signatures of Jackson and Bell gained greater importance following the departure of stalwart hooker Liam Coltman.
Timu adds talent and versatility to the backline, having impressed for the Highlanders on his return from a knee injury just over a month ago.
He formed a promising midfield combination with Thomas Umaga-Jensen, which is likely to continue for Otago.
Hill will return after playing the Super Rugby season in Melbourne, adding depth to an already quality locking group, which includes Highlanders Josh Dickson and Fabian Holland.
“We are pretty stoked to have these four men [Jackson, Bell, Timu and Hill] back on board with us again this season," Otago coach Tom Donnelly said in a statement.
"It makes the deal even better knowing that they are all local players who have progressed through the system to get to where they are today.
"They are Otago through and through, and each one of them is from a different part of the province. Bell, East Otago, Timu from Central, Hill from South and Jackson from Metro.
"These guys set a good example for developing players that hard work and dedication from a young age can lead to exciting opportunities.”
It gives Otago what looks to be the nucleus of a strong team with a handful of signings still to come.
Notably, halfback may require some attention.
Kayne Hammington is heading to Japan and understood to be unavailable for Otago, while Nathan Hastie has a long-term injury.
Otago kicks off its season on August 6 against Counties-Manukau in Pukekohe.
