"Showing nudity goes beyond social customs and norms in Poland," read part of the verdict issued by a court in Szczecin, northwest Poland. "Personal freedom ends where the freedom of another person begins."
"I completely respect the court's verdict, but at the same time I disagree with it and I will certainly appeal it," Dorota Krzysztofek, 28, told Poland's TVN24 news channel. She also said she would be contacting Poland's ombudsman, a civil rights watchdog.
The court also ruled the women would have to pay court fees of 130 zlotys (36 euro, 46 dollars). The verdict is subject to appeal.
"Perhaps men will also have to cover up their torsos on the beach?" Krzysztofek said. "I see nothing indecent about the chests of men or women," she added.
In May, policemen fined Krzystofek and her 26-year-old friend for sunbathing topless on a public beach in Szczecin.
The women went to court after they failed to pay a fine of 150 zlotys (40 euros, 55 dollars).
The case of the two women, one of whom is a model and has appeared topless in Polish men's magazines, sparked such massive media interest that a first hearing in September had to be postponed when too many reporters turned up to fit into the court gallery.
The women pleaded not guilty to indecent exposure, arguing there was no explicit ban on going topless at the beach.
They also said fellow sunbathers had not been offended, insisting that many had jumped to their defence.