One complainant objected to adverts on Rightmove and Zoopla where the property was described as a one-bedroom flat rather than a studio.
This was resolved informally and the adverts were revised.
Mortgage Solutions contacted Countrywide for further information but it has not received any comment yet.
The is the latest in a line of complaints against agents taken to the ASA in recent months
In August, a triple bill of property-related cases were informally resolved by the advertising regulator, including one about an online estate agent which failed to clarify how its charges compared to other agents.
And in September an estate agent breached advertising standards by featuring a client testimonial for an employee from his former job on its website.
