An inorganic flame retardant, magnesium hydroxide (MH) with series synergists including melamine (ME), linear novolac resin (LNR), and triphenyl phosphate (TPP) was incorporated with polyformaldehyde (POM) resin in this article. The obvious advantage of the system is that the used flame retardant and the synergists possess multiflame retarding mechanisms and multifunctions. The prepared flame retardant POM could achieve UL94 V-0 rating (1.6 mm) with optimum flame retardant/synergists formulations, showing satisfactory flame retardance. Various characterization methods including pyrolysis-gas chromatogram-mass spectrometer (Py-GC-MS) analysis, scanning electron microscope (SEM) observation, and thermogravimetric analysis (TGA), were used to investigate the interaction among the components and reveal the corresponding synergistic mechanisms. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012