Fiat stock rose despite the market overall falling, with the benchmark FTSE Mib index down 1.49 percent in midday trading.
The shares were also boosted by data showing a 5.4-percent rise in European auto sales in June, confirming a recovery in a sector badly hit by the economic crisis.
Fiat rejected the report in Manager Magazin that said Volkswagen was looking into "a takeover or partial takeover" of its Italian-US competitor Fiat-Chrysler.
The magazine said Volkswagen was particularly interested in Chrysler and its US distribution network, while the Italian side could focus on luxury cars like Fiat's Ferrari brand.
Exor, an investment company controlled by the Agnelli family which has a controlling stake in Fiat, said: "There has been no discussion on a merger of Fiat with Volkswagen".