Her specifications were very similar to that of the British-built Takasago, but with slightly larger displacement and overall dimensions, but with identical gun armament (and without the bow torpedo tubes).

On 9 February 1904, she was part of the 3rd Cruiser Squadron under the overall command of Admiral Dewa Shigetō which engaged the Russian fleet at the entrance to Port Arthur, taking some minor damage.

On 14 May, Kasagi assisted in efforts to save the crew of the battleship Hatsuse after that ship struck a naval mine, rescuing 134 survivors, and firing on Russian destroyers.

During the Battle of the Yellow Sea on 10 August, Kasagi engaged the Poltava, and participated in the unsuccessful pursuit of the cruisers Askold and Novik.

However, Kasagi was hit below the waterline by a Russian shell, which flooded a boiler room and coal bunker, killing one crewman and injuring nine others, and was forced to withdraw from combat to address the damage.

Kasagi ran aground in heavy weather in the Tsugaru Strait between Honshū and Hokkaidō en route to Akita on 20 July 1916, suffering a major hull breach in the vicinity of her second smoke stack.