The SNCF Class BB 66600 is a small class of centre cab diesel locomotives rebuilt from the earlier Class BB 66000 by fitting a slightly more powerful engine.

The locomotives were 14.898 m (48.88 ft) long and weighed 71 t (70 long tons; 78 short tons).

Powered by an SEMT 12PA4 diesel engine developing 1,100 kW (1,500 hp), they had a maximum speed of 120 km/h (75 mph).

All members of the class were fitted for multiple working and all but two had electric train heating.

Initially all 11 were allocated to Nîmes to work services to Clermont-Ferrand.