Optus added 80,000 customers in the three months to the end of March, taking its total to nearly 9.5 million.
Australia's second biggest telco had 9.49 million customers at March 31, up from 9.41 million at December 31, a rise of just under one per cent.
In the year to March, Optus added 421,000 customers, a rise of 4.6 per cent, according to figures released by Optus' parent SingTel on Wednesday.
Rival Telstra had 13.2 million mobile customers at December 31, its most recent financial reports showed.
Optus said postpaid customers make up 55 per cent of its customer base.
Its customers on 3G totalled 6.63 million, up six per cent in the three months to March, Optus said.