Optus' first-half profit has fallen 7.2 per cent and the company says revenue growth has slowed because of price competition.

Optus made a net profit of $319 million in the six months to September 30, down from $344 million in the previous corresponding period.

Operating revenue in the six months of $4.48 billion was down 3.7 per cent from $4.65 billion in the same period the previous year.

"Mobile industry growth rates have slowed as a result of price competition and mandated reduction in mobile termination rates," Optus parent Singapore Telecommunications (SingTel) said in a statement on Wednesday.

Lower equipment sales, a reduction in the mobile termination rate and the introduction of service credits with handset repayment plans contributed to the fall in revenue, SingTel said.

Optus's customer numbers rose to 9.54 million, as of September 30, but average revenue per user (ARPU) fell because of discounts on bundled plans.