"We want to open new horizons between the two countries," Hariri told a news conference at the Lebanese embassy in Damascus.
He said his three rounds of "excellent" talks with the Syrian leader were frank and based on clarity.
"There will be serious steps from our side and on the part of President Bashar al-Assad to translate this cordial and serious relationship into steps on the ground in several fields," Hariri said, without giving details.
A senior Syrian official, Buthaina Shaaban, had described the talks as constructive, cordial and transparent. Assad had extended a warm welcome to Hariri upon his arrival in the Syrian capital on Saturday.
Hariri said the talks did not cover the 2005 assassination of his father, statesman Rafik al-Hariri, but that Assad had agreed the issue now was in the hands of a special court set up in The Hague to indict and punish the killers.