The dual-stage pulse-feed anaerobic co-digestion of fat, oil and grease improved the stability of reactors to withstand high OLR of 2.71 kg VS/m3/d. The utilization of major saturated and unsaturated long-chain fatty acids (LCFAs) reached 78% and 98% in the acidogenic fermenters with consecutive organic loading, respectively. The assessment of the microbial community revealed that acidogenic Intestinimonas and Megasphaera, and acetogenic Levilinea were predominant in the fermenters due to their preeminent activities.