The former Tottenham boss was unsure of how things would pan out in Holland as Ajax were looking to sell some of their best players to bring in some cash so he weighed up his options and decided to leave.
Jol, who will be officially unveiled before the Cottagers' friendly at Swedish side Halmstad on Thursday, also revealed that he is very fond of the Premier League.
"The Premier League is the best competition in the world, and I like London very much. Fulham is a great opportunity.
"The way it is going at Ajax we cannot play for the title, or the biggest prizes.
"For the past two weeks I have been very worried about what is going to happen with Ajax.
"In the past they have paid too much for not so good players and now they have no money to invest in the squad."