From the first name Prospero.

The authors agree that this surname derives from the given name Prospero, which continues the Latin cognomen Prosper or Prosperus, consolidated in Christian times and settings as an auspicious name. E. De Felice specifies that it comes from the Latin adjective prosper(us), with the meaning of "prosperous, happy, fortunate," and that as a name it expressed the wish that the bearer have a favourable fortune. R. Brondolo agrees on its auspicious character and sums it up as "may he grow prosperous."

E. Rossoni notes that all the variants of the surname should derive, directly or through diminutive forms, from the medieval name Prosperus. As a notable historical reference, he mentions the cardinal Prospero Lambertini, who was elected Pope in the second half of the 17th century with the name of Benedict XIV. De Felice places the greatest frequency of the surname in Veneto, Emilia-Romagna, Tuscany and the centre of Italy.

Rossoni details that Prosperi is concentrated in the Bologna area, the Florence and Arezzo area, and in the strip covering the Marche, Umbria, Abruzzo and Lazio. The variant Prosperini appears in the Terni area, the Viterbo area and the Rome area, with a specific presence in the L'Aquila area, while Prosperino, very rare, seems proper to southern Italy.