Joshua Leighton, 37, of Bonython, faces 23 charges of theft for his alleged involvement in the fraud of an organisation entrusted with the money of some of Canberra's most vulnerable citizens.

Defence lawyer Jacob Robertson entered pleas on his client's behalf in the ACT Magistrates Court on Wednesday morning.

Mr Robertson said Leighton denied the allegations.

His alleged co-offenders – Timothy Stewart McLeod, 33, of Pearce, Stephen Evans, 32, and Donald Tawanda Savanhu, 36 – have also entered pleas of not guilty.

It is alleged the suspect transactions took place between 2010 and 2014 and included debit card fraud, thefts from cash machines, contractor kickbacks, and false paperwork trails.

The ACT Public Trustee is a small agency with about 30 staff. It administers the estates of dead people, and the funds of Canberra's most vulnerable, including people who are unable to manage their own affairs because of disability, illness or age.

It has repaid $1.7 million to 87 clients.

The agency has also overhauled its fraud protection strategies, and brought in corporate giant KPMG to conduct an audit, the results of which have not been made public.

A further 15 control measures, designed to minimise the risk of fraud, were introduced after an internal review, and senior managers at the office also attended industry fraud and risk training seminars.

The matters will return to court next year.