The 125 S (commonly called the 125 or 125 Sport ) was the first vehicle produced and built by Ferrari. Although preceded by Enzo Ferrari's Auto Avio Costruzioni 815 of 1940, the 125 S was the first vehicle to bear the Ferrari name when it debuted on May 11, 1947 at the Piacenza racing circuit. Like the 815, it was a racing sports car, but unlike its Fiat -powered 8-cylinder predecessor, the 125 S had a new V12 engine (the "125") like most Ferrari cars of the following decades. The 125 S was replaced by the 159 S for 1947.

The 125 S used a steel tube-frame chassis and had a double wishbone suspension with transverse leaf springs in front with a live axle in the rear. Hydraulic power drum brakes were specified front and rear.

The 125 S was powered by Gioacchino Colombo's 1.5 L (1497 cc/91 in³) 60° V12. This engine produced 118 hp (74 kW) at 6,800 rpm with a compression ratio of 8.5:1. It was a dual overhead camshaft design with 2 valves per cylinder and three double-choke Weber 30DCF carburettors