HMS Ulla Fersen was a frigate of the Swedish Royal Navy, designed by Frederik H. Chapman, and launched in 1789. She served during the Russo-Swedish War (1788-1790), most notably at the Battle of Reval. British vessels twice detained her, once in 1798 and again in 1801, with the first event resulting in a major court case bearing on the meaning of neutrality. She was completely rebuilt in 1802, and lost in a storm in 1807.