After two minutes, Alberto Gilardino had the first effort on goal, but his shot did not test the goalkeeper.
Bologna did all the attacking in the early stages and had a chance again on 10 minutes, but Alessandro Diamanti's strike just missed the target.
Alessandro Rosina had Siena's first attempt on 24 minutes, but the home side's defence were quick to react and block the shot.
Siena then took the lead against the run of play after 33 minutes through a header from Innocent Emeghara.
Panagiotis Kone equalised for the home side on 41 minutes.
Gilardino and Rosina had chances for either side early in the second half, but neither could get on the scoresheet.
Diamanti threatened to give Bologna the lead on a few occasions in the last 15 minutes, but the away team stood firm.