Pietro Ziani (died 13 March 1230) was the Doge of Venice from 15 August 1205 to 1229, succeeding Enrico Dandolo.

In his youth a sailor, he commanded a flotilla escorting the emperor Frederick Barbarossa in 1177, took also part in the Fourth Crusade and sacking of Constantinople.

Ziani established also commercial ties with the post-Byzantine states, signing in 1210 a treaty with the despotate of Epirus under Michael I Komnenos Doukas.

According to the Cronaca Altinate, he strove to maintain peace with Padua after an incident at a festival in Treviso so that Venice could concentrate on its new Greek territories.

He was succeeded by his brother-in-law, Jacopo Tiepolo, but Ziani refused to meet him and died a year later.