An LED lamp includes a heat dissipation device and a plurality of LED modules. The heat dissipation device includes a heat conductive member and a fin unit. The LED modules are attached to a top surface of a first plate of the heat conductive member. The heat conductive member comprises a plurality of posts embedded in the top surface of the first plate. Peripheries of the first and second plates are in a hermetical conjunction with each other to form a chamber containing phase-changeable working fluid therein. The first plate has a plurality of receiving recessions which are depressed downwardly from the top surface thereof and respectively receive the posts. Screws are used to extend through the LED modules to threadedly engage in the posts thereby to intimately mount the LED modules on the top surface of the first plate of the heat conductive member.