Please be aware that Rome has multiple airports and that these results are for all airports serving the city.
The best month to fly between Rome and Barcelona is September and the most expensive month to fly is February. (Average prices, based on 293 datapoints.)
The best day to arrive at Rome is Monday and it would be best to avoid Saturday, as prices are on average 156.65% higher than on Monday. (Average prices, based on 214 datapoints.)
The cheapest airline flying from Rome to Barcelona is Ryanair. They are 49% cheaper than Alitalia. (Average prices, based on 304 datapoints.)