Abstract: Leather collagen fiber network (LCFN), as a kind of protein materials, has the potential to be prepared into flame retardant filler for polymer modification. However, due to its relatively low limit oxygen index (LOI), the modification of LCFN is needed for this purpose. In this study, the modification was undertaken by retanning LCFN using dicyandiamide resin, melamine resin, acrylic resin, vegetable tannin, chromium tanning agent and aluminum sulfate, respectively. The effects of type and dosage of retanning agents on the flame retardancy of the LCFN were studied. The results showed that retanning can improve the flame retardancy of LCFN. The LCFN retanned by aluminum sulfate had the best flame retardant performance due to the highest initial decomposition temperature, the largest char yield (800 ℃), and stable and dense structure of carbon residue. Especially, when the dosage of aluminum sulfate (based on Al₂O₃) was 3%, the LOI and char yield (800 ℃) of the modified LCFN increased to 61.4% and 13.65%, respectively, which exhibited excellent flame retardant performance.