The 1905 Lancashire Cup was the inaugural year for the rugby league Lancashire Cup competition. The cup was won by Wigan who beat Leigh in a replay at Wheater's Field, Broughton, Salford by a score of 8-0.

Following the great schism of 1895 which led to the formation of rugby league there was an interest in a competitive competition for clubs based in Lancashire. Prior to the breakaway from rugby union this was something that had been discouraged as it was feared that competition would lead to professionalism, as had happened in other sports like Association Football.

There appears to be very little, if any, details of how this came about, or any details of any of the instigators or of any campaign, but the County Cups became the last part of what would become known as the four cups.

The competitions were played on the same basis as was the Challenge Cup, i.e. a free draw with matches played on a sudden death straight knock-out basis, and with the final played (usually) on a neutral ground.

• 1905–06 Northern Rugby Football Union season