Sony also began Sunday a phased restoration of its Qriocity movie and music services which share the PlayStation Network's server, said Sony Computer Entertainment Inc. spokesman Satoshi Fukuoka.
Limited services will also resume in Australia, Canada, New Zealand and the Middle East, and Sony said it will start restoring the service for users in Asia soon.
Sony's PlayStation network is a system that links gamers worldwide in live play. Sony shut it down on April 20 after discovering a hacker attack.
Sony said personal data, including credit card numbers, may have been stolen. But the company said Sunday it had not received any reports of the stolen information being used illegally.
Kazuho Hirai, chief of Sony Corp.'s PlayStation video game unit, said in a statement that the company has beefed up security measures to protect customers' personal data.
While the partial service allows users to enjoy video games and online chat, Sony said consumers still cannot buy video games or other content by using credit cards.
"While we understand the importance of getting our services back online, we did not rush to do so at the expense of extensively and aggressively testing our enhanced security measures," Hirai said.
Among the 100 million user accounts, Sony said about 92 million can access the limited PlayStation network service.
The network serves both the PlayStation video game machines and Sony's Qriocity movie and music services. It is a system that also allows users to upgrade and download games and other content.
Sony spokesman Sosuke Kamei said the company's probe into the hacker attack was ongoing. He declined to give details on the investigation.
Sony was under heavy criticism over its handling of the network intrusion. The company did not notify consumers of the breach until April 26 even though it began investigating unusual activity on the network from April 19.
Last month, U.S. lawyers filed a lawsuit against Sony on behalf of lead plaintiff Kristopher Johns for negligent protection of personal data and failure to inform players in a timely fashion that their credit card information may have been stolen. The lawsuit seeks class-action status.
Since the shutdown of the PlayStation Network on April 20, Sony's share price has dropped nearly nine percent to close at 2,241 yen ($28) on Friday.