Tetrabromobisphenol A (TBBPA) is a brominated flame retardant widely used in electronic plastics, but its effects on invertebrate-mediated plastic biodegradation remain unclear. This study investigated the impact of TBBPA on the biodegradation of rigid polyurethane (RPU) by Galleria mellonella and Tenebrio molitor larvae, and the effects of both larvae on the chemical transformation of TBBPA. Results showed that TBBPA inhibited the uptake of RPU by both larvae, resulting in a decrease of intestinal protein-like fluorescence intensity, reduced the concentrations of certain metabolic by-products of RPU, and inhibited the growth of RPU degradation related bacteria. Most TBBPA was excreted by both larvae, and a small fraction was transformed into less toxic brominated organic compounds. Sequencing analysis suggested that Enterobacteriaceae, Enterococcus, and non-dominant gut bacteria might play a role in TBBPA degradation. This study provides detailed insights into the interactions involved in the biodegradation of TBBPA-containing RPU by two invertebrate species.