The 1920–21 Lancashire Cup competition was the thirteenth playing of this regional rugby league competition. Broughton Rangers beat Leigh in the final at The Willows, Salford by a score of 6–3. The attendance at the final was 25,000 and receipts £1800. Both set new records at the time; the previous highest attendance was 20,000 in 1911.
Background
The number of teams entering this year's competition was increased by 2 from the previous season's 12 to 14 with the introduction of two junior/amateur clubs Wigan Highfield (who would become members of the league in two years time), and Cumbrian team Askam. This enabled the competition to be run with only 2 byes in the first round.