The departure of some lawmakers from the ruling party will leave the party with some 90 lawmakers within the 300-seat parliament.
More than 30 lawmakers of the Saenuri Party, who have been at odds with Park, have vowed to leave, arguing the party's current leadership refuses to embrace reforms despite the corruption scandal and impeachment crisis.
"We've reached a conclusion that conservatives' reform through the Saenuri Party is impossible", Yoo Seung-Min, an eminent lawmaker among the dissenters told journalists.
A split would also complicate a possible run by outgoing UN Secretary General Ban Ki-Moon, who had been widely expected to compete as a centre-right candidate on the Saenuri ticket.
Thirty-five lawmakers have agreed to break away from the party on December 27, the group said, adding they will try to convince more parliamentary members to join them.
Their departure will leave the party with some 90 lawmakers within the 300-seat parliament and relegating it to second place behind the liberal Democratic Party within the National Assembly.
The group crossed party lines to join opposition parties in passing a motion to impeach Park this month.
Park is accused of colluding with her friend Choi Soon-Sil to strong-arm large companies like Samsung into handing over tens of millions of dollars to two dubious foundations Choi allegedly controlled and plundered.
Park is also accused of ordering aides to leak state documents to Choi, who has no official title or security clearance, and allowing her to meddle in some state affairs, including the appointment of top officials.
The case is now being considered by the constitutional court, which has up to 180 days to rule on the validity of the impeachment that charged Park with multiple criminal and constitutional violations -- ranging from bribery to abuse of power.
If the justices confirm impeachment, Park will be permanently removed and elections must be held within 60 days -- meaning a ballot could be held as early as late March.
The split will drastically reduce the chances of the conservative party winning the presidential election.