The vehicle shown actually cost £14,450, with an optional ebony coloured roof.
The ASA noted the headline price of £13,950 did not correspond to the car in the accompanying photograph.
Alfa Romeo offered to add the word "from" to the headline price, but the ASA considered that would not go far enough, because the CAP Code for advertising stated that prices quoted should correspond to the vehicles illustrated.
The ASA said: "We acknowledged that the price of the model featured was given in small print at the bottom of the ad but considered that was likely to contradict the impression given by the headline and photograph that the model featured could be purchased for £13,950.
"We told Alfa Romeo to ensure that headline prices were preceded by "from" if they were starting prices for a range, and that quoted prices corresponded to vehicles illustrated.
"We advised them that it would be acceptable to quote both a "from" starting price and the price of the model featured, providing both prices were given equal prominence."