Onstaborg (also known as Nieuw Onsta in Dutch, meaning "New Onsta") was a borg in the village of Wetsinge, Groningen, Netherlands.

The borg was built around 1500 by the family Onsta (also known as Onseda, Onsitha or Onsatha).

The Onsta family also owned an Onstaborg in Sauwerd.

In 1658 the borg was sold and refurbished.

There is no trace left of the borg or its grounds.