Adult occupant
The B-Class is fitted as an option with Mercedes Benz's 'PRE-SAFE'® system which primes the restraint and protection systems in readiness for a collision. In Euro NCAP’s frontal and side barrier impacts, the PRE-SAFE® System was not activated. In the frontal impact, the B Class scored maximum points for its protection of the driver with all body areas being well protected. For the passenger, good protection was provided in all body areas except for the lower legs, protection of which was rated as adequate. Mercedes-Benz showed that good protection would also be provided to the knees and femurs of occupants of different sizes and to those sat in different positions. In the side barrier test, the B Class scored maximum points, all body areas being well protected. In the more severe side pole test, protection of the chest was adequate and that of all other body areas was good. The front seat and head restraint provided good protection against whiplash injuries in the event of a rear end collision.

Child occupant
In the frontal impact, forward movement of the 3 year dummy, sat in a forward facing restraint, was not excessive. In the side impact, both dummies were properly contained within the protective shells of their restraints, minimising the likelihood of dangerous head contacts. The passenger airbag can be disabled only for Mercedes Benz child restraints if the car is equipped with an optional, automatic-detect system known as CPOD. The system does not meet Euro NCAP's requirements and was not rewarded. The dangers of using a rearward-facing child restraint in the passenger seat without first disabling the airbag are clearly explained in the car.

Pedestrian
The bumper scored maximum points, providing good protection to pedestrians' legs in all areas tested. However, the front edge of the bonnet provided poor protection and scored no points. In most areas likely to be struck by the head of a child, the bonnet provided good protection but was predominantly poor in those areas where an adult's head might strike.

Safety assist
Electronic stability control is standard equipment and met Euro NCAP's test requirements. A seatbelt reminder is standard for the driver, passenger and rear seats. A driver-set speed limitation device is available as an option but did not meet Euro NCAP's fitment requirements for assessment in 2011.