For the 1954 Spanish Grand Prix Rosier entered the new Maserati 250F, and finished in seventh position. In Rosier returned to entering only a single car for himself. He retired in Monaco and finished ninth in both Belgium and the Netherlands. For Rosier again entered the Maserati. He started the season with a retirement at Monaco before finishing eighth in Belgium and sixth in France. After starting twenty-seventh in Britain, Rosier retired on lap twenty-three when his electrics failed. The 1956 German Grand Prix, where Rosier finished a strong fifth, proved to be the last Grand Prix of Ecurie Rosier because Louis Rosier died of injuries he sustained in a crash at the Montlhéry track, south of Paris, France, on 7 October 1956.