The 1925 Isle of Man Tourist Trophy was the second and final year of the Ultra-Lightweight class for motorcycles of 175 cc capacity.
After numerous retirements in 1924, Wal Handley won the Junior TT race over six laps of the Mountain Course on a Rex-Acme motorcycle at an average speed of 65.02 mph (104.64 km/h).
During the Lightweight TT race, Wal Handley led the first two laps by over two minutes from C. W. "Paddy" Johnston, riding a Cotton, but a puncture caused Handley to slip off his motorcycle at Signpost Corner.
The Senior TT race was sensationally won by Howard Davis while competing against the works teams with a motorcycle of his own manufacture, an HRD, in 3 hours, 25 minutes, 8 seconds at an average speed of 66.13 mph (106.43 km/h).
A new lap record was posted by Jimmie Simpson, in 32 minutes and 50 seconds and an average speed of 68.97 mph (111.00 km/h) on an AJS motorcycle, but he failed to finish.