Tractors, mini-diggers and plant machinery have been stolen in eight separate thefts from farms near Bath in the last month.
Police say all the machines were taken in overnight raids.
The equipment was stolen from farms in Clutton, Marksbury, Saltford, Shoscombe, Bathampton and Weston.
Officers believe the same gang is behind all the raids, and are warning farm owners to make sure their equipment is secured.
Sergeant Stefan Perkins said: "We are encouraging people to not become complacent when it comes to security.
"On many occasions people leave machinery unsecured in easily accessible locations."