Osmani decided to dissolve parliament after members failed to agree on a new president, opening the way for a third election in just over a year.
The court's ruling on Wednesday, which comes after Prime Minister Albin Kurti took the matter to court, means that parliament has 34 days to elect a new president. If it fails again, new elections must be held within 45 days.
Kosovo was plunged into a political crisis early last year as a result of an inconclusive parliamentary election, which in turn forced new elections in December.
