Princess Peach is shown to be Mario's close companion since childhood. Mario saves Peach quite often and she usually will bake him a cake or kiss him upon her rescue. Since Peach's debut appearance, the two have been largely speculated to be in a romantic relationship. This is confirmed in the official European Mario website, in which Peach is listed as Mario's girlfriend.
In Luigi's Mansion, she sends Toad to help search for his brother,and in Mario Party 5, Peach and Mario are called "Cutest Couple". They also share chemistry together in Mario Superstar Baseball and Mario Super Sluggers, as they are "buddy players". Mario Power Tennis even goes as far as showing Mario himself telling Peach of his love for her in Peach's victory scene. Peach responded with a smile and blew a kiss. Also, in Mario's victory scene in Mario Power Tennis, Peach gives him a small kiss on his cheek. They both show deep devotion to each other as depicted in many of the games, especially in the Paper Mario series. In the comic "Warios Weihnachtsmärchen", published in the German Club Nintendo magazine, it is even revealed that they spent their graduation ball in school together, and that Peach decided in favor of Mario and against Wario. Mario and Peach are the Secret Staff Ghost for Rainbow Road in Mario Kart: Double Dash!!. The official guide describe them at this: Aw, isn't that cute? Mario and Peach are together again, zipping down the Rainbow Road and leaving the player coughing up their dust.
In the first Paper Mario, one of the Toads tells Mario to take Peach on a date to Shooting Star Summit. For the official guide of Yoshi's Island DS, in the description for the level Baby Mario and Baby Peach: Dynamic Duo, Nintendo metioned that before the "romantic entanglements" in their adult lives, they teamed up as babies to stop evil. Also the official quide for Mario Party 8, as well as Kersti in Paper Mario: Sticker Star, stated that Peach is apple of Mario's eye. Rosalina in Super Mario Galaxy even referred to Peach as Mario's 'Special One'.
In Super Paper Mario, if Mario is used at the beginning of Chapter 7-3, Luvbi asks, "are you Peach the lady friend of Mario?" Mario nods his head no in response. Luvbi, implies that she "looms large in his regard," however, as well as that it may be "A one-sided crush"
In the credits of Super Mario 3D Land and New Super Mario Bros. 2, he embraces Peach as he takes her back to her castle.