The news item discussed the dispute between the Scottish Government and Mr Salmond, the former first minister, and the Holyrood inquiry which was then ongoing.
It was broadcast on the day Mr Salmond was due to appear before MSPs on the inquiry committee.
However, he had announced he would not be attending following a row over his written evidence, which was redacted against his will amid legal concerns.
Speaking to the BBC, Ms Davidson said the dispute raised questions about whether Scotland’s democratic institutions are corrupt, and accused the Scottish Government of running riot over the parliamentary right to scrutiny.
This sparked a listener complaint “about a lack of due impartiality” and the choice of Ms Davidson, who now sits in the House of Lords, as the only interviewee.
The BBC said its decision to interview Ms Davidson was prompted by “significant developments in the story” resulting in Mr Salmond not appearing before the committee as planned.
The broadcaster said it had repeatedly attempted to interview a representative from the SNP but the party did not respond.
It also said context was provided in other ways, and cited later coverage on Radio 4 which “included the SNP’s position in detail”.
But Ofcom found the BBC had failed to preserve due impartiality.
In a written ruling, it said that “given the gravity of Ruth Davidson’s accusations regarding the Scottish Government, her strong and continued criticism and the fact that she was able to express her views at length, we did not consider that alternative perspectives were given due weight within the programme”.
It also said it “did not consider that the BBC had reflected, and given due weight to, an appropriately wide range of significant views in clearly linked programmes”.
Ofcom said it took careful account of the broadcaster’s and audience’s rights to freedom of expression in reaching its decision.