The thermal properties of residual char of basalt fiber (BF) reinforced intumescent coating (IC) obtained after high temperature burning were studied. Seven intumescent coating formulations were prepared in which the weight percentage of basalt is varied from 0 to 3 wt. of the total formulation. The effects of BF weight percentage on fire resistance of IC, and char morphology and composition were also studied. The heat barrier effect was analyzed by using a Bunsen burner (ASTM E119). Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) were used to investigate the IC and residual chars. Furthermore, the thermal conductivity was calculated as a function of temperature to compare the structure and properties of char residues. Intumescent chars with different weight percentages of BFs (in particular formation of pores of different sizes) were firstly verified. The interpretations were not in agreement with the thermal conductivity data. IC-B3 is the formulation that contains 3 wt. of BF had thermal conductivity value of 0.114 Wm �1 K �1 . The morphological study confirmed that 3 wt. of BF formed a network that protected the underlying steel substrate from temperature rise in the event of fire. TGA results showed that BF reinforced formulations; IC-B3 had 36.26 of residual weight at 800 °C as compared to IC-B0, which had 27 wt.. Elemental analysis showed that IC-B3 had enhanced carbon content of 63.1 in the residual char. Pyrolysis-gas chromatography-mass spectrometry (Pyrolysis-GCMS) revealed that IC-B3 suppressed the release of toxic gases as compared to IC-B0 and the average percentage of released gases decreased from 83.3�57.1. © 2019 Elsevier B.V.