Brookfield Renewable UK applied to develop a site at Larbrax, near Leswalt in Wigtownshire.
Dumfries and Galloway Council's landscape architect objected to the plans, claiming it would have an adverse visual impact on the surrounding coastal area.
Scottish Natural Heritage also raised "significant and serious concerns".
A spokesman for Brookfield Renewable UK said: "It is disappointing that the Dumfries and Galloway planning committee have failed to recognise both the many positive long-term economic benefits the Larbrax Wind Farm would bring to the Wigtownshire area, and also the limited effects of the proposal.
"We appreciate that there is frustration locally following the decision and we would like to thank local residents and businesses for the time and support that they have afforded the project over the last three years.
"We maintain our position that this is an acceptable and beneficial scheme and we will now carefully consider our next steps."
Meanwhile, a separate proposal for a wind farm at Gass Farm, north-east of Glenluce, has been approved.
Councillors backed WilloWind's plans for the nine-turbine development, subject to strict conditions.
Plans to build eight new wind turbines in the far south-west of Scotland have been rejected by councillors.