Khalifa was stopped by Romanian police in July 2024 after allegedly smoking cannabis on stage at the Beach, Please! Festival in Costinesti, a coastal resort in Constanta County.
Prosecutors said the rapper, whose real name is Cameron Jibril Thomaz, was found in possession of more than 18 grams of cannabis, and that he consumed some on stage.
The Constanta Court of Appeal handed down the sentence on Friday after Khalifa was convicted of "possession of dangerous drugs, without right, for personal consumption", according to Romania's national news agency, Agerpres.
The decision came after a lower court in Constanta County in April issued Khalifa a criminal fine of 3600 lei ($A1250) for "illegal possession of dangerous drugs", but prosecutors appealed the court's decision and sought a higher sentence.
Romania has some of the harsher drugs laws in Europe. Possession of cannabis for personal use is criminalised and can result in a prison sentence of between three months and two years, or a fine.
It is not clear whether Romanian authorities will seek to file an extradition request, since Khalifa is a US citizen and does not reside in Romania.
The 38-year-old Pittsburgh rapper rose to prominence with his breakout mixtape Kush + Orange Juice.
On stage in Romania last summer, the popular rapper smoked a large, hand-rolled cigarette while singing his hit Young, Wild & Free.
