Although Jeddah is by far the most cosmopolitan and modern city of Saudi Arabia, nightlife in Jeddah probably isn't the nightlife you know from you're own country, there are no nightclubs or disco's here. Because of it's Islamic religion alcohol is forbidden (even in the Jeddah hotels) in Saudi Arabia and severly punished when used or handled.
The Jeddah nightlife starts after the sunset prayer, people dine out in one of the Jeddah restaurants (a favorite among Saudi's), walk around enjoying the beach/sculptures, smoke a traditional waterpipe, play cards or drive around and show of the car. There are many good cafes in Jeddah where people talk or watch other people. Or go to the cinemas, festivals or events.
Enjoy the hospitality and friendliness of Jeddah and it's people! Enjoy your stay in Jeddah and if you need a hotel in Jeddah, visit the Jeddah Hotel page.