Prior to this years Mille Miglia the responsibility for running the Alfa Romeo cars was brought in house under Alfa Corse, and Vittorio Jano was forced out of the team. Enzo Ferrari was still in charge of the racing team but new levels of bureaucracy were added that would cause Ferrari to leave on his own. Three new 8C 2900B Alfas were prepared for the event , to be driven by Pintacuda, Farina and Biondetti. Biondetti's cars was fitted with an experimental 308 engine which had slightly more power. Clemente Biondetti was born in a small village in the hills of northern Sardinia and grew up there. He was a late starter in racing as his career did not begin until his family moved to Florence in the 1920s. He would turn forty later that year. Delahaye once again entered two cars, this time with 4.5-litre V12s to be driven by Dreyfus and Mazaud. Delahaye used lightweight alloys extensively in both the engine block and heads of their new V12. In an age when cast-iron engines were the norm, the use of aluminum alloy for the heads and magnesium alloy for the engine block was quite a daring move. Talbot entered a single car for Rene Carriere and BMW entered four of their new 328s.
Unlike last year the weather conditions were perfect when the first cars were sent off at 2 a. m. with Pintacuda, already a two-time winner again streaking into the lead setting another new record on his way to Bologna. Following Pintacuda was Dreyfus' Delahaye and Biondetti's Alfa. Pintacuda held his lead into Rome now over Biondetti, Dreyfus being delayed by a stone through the radiator which would doom it the fourth place. At Terni Pintacuda paid the price for his record run with early brake problems which required a 14 minute stop for repairs allowing Biondetti in to the lead. Pintacuda would not give up so easy and put on an incredible display of driving but try as he might he could not make up the last two minutes on Biondetti who held on to claim the win. In a harbinger to the future two BMW 328s finished eighth and tenth.
The 1938 event was marred by an accident involving one of the smaller entrants. Just after leaving Bologna a Lancia Aprilia, drive by two amateurs left the road and somersaulted into the crowd after crossing a tram-line. Ten spectators were killed outright including seven children. Twenty-three others received serious injuries. The cause of the accident was never completely established, nonetheless the following day the Italian government, bowing to public pressure, banned the Mille Miglia from racing on public roads in built-up areas. The ban was still in effect in 1939 and no race was held that year.