The latest financing boosted SAIC Mobility Robotaxi's value to more than $1 billion, the statement said.
Momenta did not disclose the size of its investment in SAIC Mobility Robotaxi, which tapped Momenta last year to jointly develop autonomous technology.
The two companies last year began offering robotaxi test rides to the public in a Shanghai district and then in Suzhou.
Momenta's investment in SAIC's autonomous unit comes as startups have been pouring billions of dollars into autonomous technology, aiming to take an early lead in commercializing autonomous driving.
Earlier this month, China search engine giant Baidu Inc said it obtained permits to operate fully driverless robotaxi services on open roads in two Chinese cities -- the southwestern municipality of Chongqing and the central city of Wuhan.
The permits allowed commercial robotaxis to offer rides to the public without human safety drivers in the car.
In April, Baidu and Toyota Motor Corp-backed Pony.ai said that they received permits in Beijing to deploy robotaxis without safety drivers in the driver's seat on open roads within a 60 sq km area. The Beijing permits still require them to have a safety driver in the passenger seat, however.
($1 = 6.7858 Chinese yuan renminbi)
(Reporting By Norihiko Shirouzu in Beijing; Editing by Bernadette Baum)