كتب : Omar AbdelAziz
Ismaili agreed to loan out their top marksman until the end of the season after he penned a contract extension that ties him with the coastal club until 2014.
However, Saudi champions Hilal have an option to extend the deal for another season as the transfer fee is reported to be around $450,000.
Ali could make his debut with the Riyadh giants in a Saudi Crown Prince tie with Najran next week.
He joined Ismaili from Asyut Petroleum in the summer of 2009, scoring 16 goals over two seasons for the Dervishes.
The 24-year-old becomes the second Egyptian to play for Hilal after former Egypt sweeper Ashraf Kasem, who had a spell in Riyadh in the 90s.