Class 251 may refer to:
Trains
British Rail Class 251, the motor car for the Blue Pullman trains. DB Class 251, a narrow-gauge diesel-hydraulic locomotive built for the Deutsche Bundesbahn. DR Class E 251, East German electric locomotives used on Deutsche Reichsbahn. Renfe Class 251, a class of electric locomotives operated by Renfe.
Submarines
No.251 class auxiliary submarine chaser, a class of submarine chasers used during World War II in the Imperial Japanese Navy.