Pioli, 45, has replaced Pierpaolo Bisoli, who was sacked yesterday after a string of poor results.
The former Palermo coach, who has signed a two-year contract with the Emilia-Romagna outfit, told the Italian media today: "I am very happy to have joined Bologna.
"I am enthusiastic and convinced that this group has the resources to defend its Serie A status.
"It's not going to be an easy task but I'm certain that this group can finish in a respectable position."
Last weekend's 2-0 defeat at Udinese dropped Bologna to the foot of the standings. The Rossoblu have mustered just one point in their opening five games, with a lack of goalscoring their main problem.
Pioli, who has also coached at Parma and Chievo, added: "Time is needed. We cannot expect to make immediate improvements but the team's growth will have to be constant.
"We will need to find balance and put the players in the best condition to give their best.
"The most important thing right now is to lift the players' morale.
"After several negative results, they have lost self-confidence and conviction, and they need to recover that as soon as possible."
Pioli's first game in charge will be against Novara on October 16.