An LED lamp bulb includes a heat sink carrying LEDs, a radiation fin set including multiple radiation fins radially arranged around the heat sink, an insulative lamp bulb base affixed to the bottom side of the radiation fin set, a light-transmission bulb shell having retaining lugs equiangularly spaced around the bottom open side thereof, and a retainer rim set between the radiation fin set and the light-transmission bulb shell and having protruding strips equiangularly spaced around an inner perimeter of a front wall thereof and respectively plugged into the gaps between each two adjacent ones of the radiation fins and retaining notches equiangularly spaced around an outer perimeter of a back wall thereof and respectively forced into engagement with respective retaining lugs of the light transmission bulb shell.