The district court of Odense found the director, the company Dan-Bunkering and its parent company guilty of selling a total of around 172,000 tonnes of jet fuel to two Russian companies on 33 occasions between 2015 and 2017.
The fuel, worth nearly 90 million euros, was then delivered to Syria, where it was used to power Russian fighter jets.
The two Danish companies were fined a total of 34 million kroner (4.6 million euros).
The chief executive of Bunker Holding, Keld Demant, was given a suspended sentence of four months.
Demant made no comment as he left the court, according to an AFP correspondent at the scene.
The prosecution had requested a sentence of two years in prison and fines of 400 million kroner, in a rare trial over violating the EU embargo for Syria.
The company and its director pleaded not guilty, arguing that they could not control what their Russian clients, who were not affected by the sanctions, did with the fuel.