The punctuality of buses in Sydney's inner west has worsened since a private company replaced the state-owned operator of services last year, new figures show.

The Berejiklian government repeatedly cited poor performance of buses run by the State Transit Authority (STA) in "region six" in the inner west as justification for privatising services there.

But data from NSW's transport agency shows the private operator, Transit Systems, has failed to beat the key performance measure of 95 per cent of buses running on time every month since it took over the contract in July last year.

Bus services in Sydney's inner west were privatised last year. Credit:Peter Rae

And its punctuality has slipped noticeably in recent months. The on-time running of buses operated by Transit Systems averaged 90.5 per cent between January and April, which was worse than the 93.5 per cent by the government-owned STA in the same period a year earlier.