At the opening of the Finnish war Adlercreutz was appointed "Ofverste" commanding the 2nd brigade under Klercker. He replaced Gustaf Löwenhielm as Wilhelm Mauritz Klingspor’s Chief of Staff on 14 April. Adlercreutz distinguished himself in action at Siikajoki, 18 April, and at Revolax, 27th. On 24 June he forced the Russians from Nykarleby. As CO of the Northern ‘Army’ he drove Raevsky from Lappo in a brilliant action on 14 July, then defeated the Russians again at Alavo in August. At the end of that month he was appointed to command the ‘Finnish’ Division under Klingspor. Forced to retreat due to the Swedish victories not being exploited, he was severely defeated by Nikolay Kamensky at the Battle of Oravais 14 September, which obliged him to abandon Finland.