Shane Rattenbury said the government-owned shareholdings had "escaped his attention".

"We, as the Greens, of course ... have sought over the years to bring a range of ethical investment filters onto the ACT government investment portfolio. I was not aware of those particular ones, but you've now drawn it to my attention and I can assure you that I will be taking that up with the Treasurer in order to clean up the ACT's investment portfolio," Mr Rattenbury said.

"I don't think that is a place that we should be seeking to benefit from, from an investment portfolio point of view."

The opposition spokesman on gaming, Mark Parton, questioned Mr Rattenbury about the shareholdings in an ACT budget estimates hearing on Thursday.

The ACT government directly holds shares in poker machine manufacturer Aristocrat Leisure, online gambling companies Pointsbet Holdings and Tabcorp Holdings, and Vici Properties, a New York-based real estate investment trust which owns casinos and hotels across the United States, including Caesars Palace, Las Vegas.

Mr Parton later told The Canberra Times the ACT government could not have it both ways, advocating to reduce gambling and investing in companies which facilitate it.

"It's really a case of 'do as I say, not as I do', and isn't that the theme for this government on so many issues? They would win the virtue-signalling gold medal hands down. But when it comes to walking the walk on these things, apparently they're not able to do it," Mr Parton said.

Mr Parton said if a private company or a bank held a similar share portfolio, Mr Rattenbury would advocate a boycott.

"I'm astounded that after the Greens MLA Caroline Le Couteur had already called this out in a previous hearing, I'm a little surprised that Mr Rattenbury professes not to know anything about it," he said.

Ms Le Couteur, a former parliamentary colleague of Mr Rattenbury, raised the issue in 2017, telling The Canberra Times the government needed to do more to ensure taxpayer funds were being directed towards "ethical ends".

"We know gambling addiction causes real and significant pain for Canberrans and their families - and that we need to do much more to reduce gambling harm in the ACT," Ms Le Couteur said at the time.

"As a start, the government should consider extending these 'negative screening processes' to gambling companies."

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Mr Rattenbury said in a statement after the hearing his focus in the previous Assembly was on the need to divest from fossil fuel companies.

"I am grateful for Mr Parton drawing this to my attention. I will raise with Chief Minister [Andrew Barr] the need to make changes so that the ACT divests from shareholdings in companies that derive profits from gaming," he said.

Ms Le Couteur's push for the ACT government to divest from gambling companies came after the territory divested nearly half of its interests in major fossil fuel companies in 2015 after lobbying from 350.org. Labor backbencher Suzanne Orr was a part of that push before she entered parliament.

A budget estimates hearing was told earlier this week the ACT was on track to completely divest of its fossil fuel shareholdings by the end of the year.

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