It happened on the A75 near Ram Hill, Castle Douglas at about 5.20 pm on Monday.
The bottle was thrown from a black Kia style four by four and hit and smashed the window of a red Audi A3 which was travelling in the opposite direction.
The Audi driver was shocked but not hurt and the black Kia continued on westwards without stopping.
Police are keen to trace the occupants of the black car and PC Robert Butcher said: “The consequences of this completely reckless act do not bear thinking about and this could have caused a serious accident.
“We would like to hear from anyone who may have witnessed this incident, or were travelling on the A75 near the Ram Hill, if they can help us identify the offending vehicle and driver. Callers can call us on the 101 number and should use the reference number PDG 0095370518.”