On 5 July 2008 Comotto signed for Serie A club Fiorentina for €4.8 million (but also cost "La Viola" an additional €198,000 as other fee) A bad injury excluded Comotto from the Champions league squad list for 2008. He made his Viola debut on 21 September 2008 in Fiorentina-Bologna, which finished 1–0. He also made his debut in the Champions League in the first leg of the qualifiers against Sporting Clube de Portugal on 18 August 2009 in the Stadium Jose Alvalade. He was the starting right-back in 2008–09 and 2009–10 season, but lost his place to Lorenzo De Silvestri in 2010–11 Serie A season. That season he only started 16 times and only re-picked by coach in October after he criticized his squad is a reason for bad results.