A Canberra man says he is still in shock after his 17-year-old Maltese was put down by ACT authorities just 24 hours after going missing.

Drago Gvozdanovic said his dog Izzy wandered out of his yard on June 10 and his attempts to find her failed.

After receiving a call from his sister one day later notifying him Izzy had been located, he contacted the vet in the hope of being reunited with his pet.

But he was informed that she had been killed.

"I was clearly, at that moment, a bit shocked and quite angry and started asking 'who killed my dog and why?'," he said.

"I'm still in shock. I don't know what to make of the situation."

Mr Gvozdanovic said just after Izzy went missing, he registered her as lost on the ACT Government's website and with the RSPCA.

She was microchipped, wearing a coat and was clearly identifiable as a pet, he said.

"She was just an old dog, she's not a wild dog," he said.

"She couldn't survive without someone looking after her, she's not able to be running wild."

Izzy was blind, had lost teeth and was partially deaf due to old age.

Seven-day impound policy to allow time to find owners

The Kambah resident said he had checked Domestic Animal Services (DAS) policies, which said impounded dogs were kept for seven days to allow time to search for their owners.

"I was very confident that if my dog ended up in the ACT Government system, I had plenty of time to ensure I could get her before any of those actions would be taken," he said.

He said despite the vet advising him Izzy had not suffered life threatening injuries, an ACT ranger had ordered the dog to be put down.

"I'm not deluded in thinking she wasn't approaching that moment when I would have to make those decisions, but it wasn't on Sunday. She was still happy in my opinion," he said.

"They say the animal does not really feel anything, but I still would have liked to have been there at that time.

"When you have something for 17 years there are rituals and habits in your life that you develop over this animal.

"So even though this animal's gone, I'm still opening the laundry in the morning to let her out."

Mr Gvozdanovic said he knew Izzy was old and he would soon have to make some difficult decisions, but those decisions should not have been made for him. ( Supplied )

In a statement, the ACT Government's city services directorate said the dog was handed in on Sunday June 10 and appeared to be in poor health.

"Its coat was highly matted and it was found to be deaf and blind, with both eyes ruptured and needing significant treatment," the statement read.

The directorate said the contact details found on the microchip were not current and a number of attempts to contact the owner had failed.

"After further liaison between DAS and the treating veterinary surgeon the dog was euthanised."

The issue was raised in Assembly Estimates this morning, and Mr Gvozdanovic was in attendance.

The ACT's director of city presentation, Stephen Alegria, told him the matter was being looked into.

"Sorry about what's happened," he said.

"We're investigating this matter very seriously, so I think it's probably not very helpful to try to predict the outcome."

Demand for answers and consequences

Mr Gvozdanovic has demanded answers about why his dog was put down in such a short period of time and before he was able to be consulted.

"I also want appropriate consequences for anything that was done that shouldn't have been done and I believe something has gone majorly wrong here," he said.

"I hope this is a one off … I hope animals aren't being killed at the convenience of the Government.

"I believed that by registering her details and having a seven-day timeframe to react was sufficient to deal with this situation but that was taken out of my hands."

The ACT Opposition has also demanded answers, with urban services spokeswoman Nicole Lawder writing to City Services Minister Meegan Fitzharris requesting an explanation of the decision.

DAS is also investigating the incident and has spoken with Mr Gvozdanovic.