Ubaldo Ranzi (18 July 1970) is a former Italian decathlete and bobsledder who competed in the late 1990s and the early 2000s.

Born in England to an Italian father and a British mother, he won a gold medal in the two-man event at the 1999 FIBT World Championships in Cortina d'Ampezzo and won a silver medal (with Gunther Huber), in 2000 always in Cortina d'Ampezzo.

Before starting his bobsleigh career he collected 6 caps in Italy national athletics team from 1993 to 1996.

While waiting for the counter-analysis, he was allowed to compete in the world bobsleigh championships, a sport in which he had only four months of training.

Going as a reserve in the two-man bob, he incredibly won the world gold medal as he found himself replacing the titular brakeman Enrico Costa injured in the heat.