Sarah Rochira spoke after inspectors ordered a newly-opened home in Conwy county to carry out urgent improvements.
They claimed parts of Merton Place care home in Colwyn Bay were not properly cleaned and had unpleasant smells.
Clwyd Alyn Housing Association says it has since made changes to its home which opened in September last year.
A spokesperson said that although officials have challenged some of the report's findings the association's board has "determined that a high priority" be given to acting on the inspectors' findings.
The report was carried out by the Care and Social Services Inspectorate Wales (CSSIW) last September.
Ms Rochira says anyone who is in a care home has a right to be safe, well cared for and listened to.
She is calling on inspectors to make sure that their recommendations are put into place in care homes across Wales.
"I've seen for myself that we have some wonderful, really good residential social care," she told BBC Wales.
"But I also know that some of our residential social care is failing older people and that is quiet simply unacceptable."
Standards at some care homes are unacceptable and need to improve, says the older people's commissioner for Wales.