Ulster made it back to back wins at the start of the Guinness PRO12 with a three tries to one win in Italy.
They pressed right at the end for a fourth bonus point securing try, but instead it was Treviso who had the final say with a try in injury time.
Ulster moved second in the table, a point behind Glasgow Warriors who have a maximum 10 points.
The Irish Province made the perfect start with a try after four minutse through Irish centre Luke Marshall, converted by Ruan Pienaar.
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But the remainder of the half saw some sloppy play with too many penalties conceded and no clincial edge.
Pienaar kicked one penalty from two attempts while Tomasso Allen kicked two from three for the hosts to leave Ulster 6-10 ahead at the break.
Former Ulster player and Samoan lock Filo Paulo was sin-binned on 49 minutes and Ulster took advantage in full.
Captain Rob Herring crossed from a lineout and drive and Pienaar went over for a try which he converted to make it 22-6.
But Ulster failed to push on, Herring was sin-binned himself and in spite of a hard push for the bonus point try, it was Treviso who had the final say with a try for Tommaso Benvenuti.