Preparation and characterization of lamellar magnesium hydroxide (Mg(OH) 2 ) thin films on cotton fabrics are reported in this paper. Mercerized cotton fabrics were treated with citric acid, so carboxyl groups were introduced to the surface of the fabrics. Mg(OH) 2 seeds were first adsorbed on the citric acid-treated cotton fabrics and then Mg(OH) 2 thin films grew on the fabric through secondary growth method. Kinetics and isotherm studies found that the adsorption of Mg(OH) 2 seeds on citric acid-treated cotton fabrics followed pseudo second-order kinetic model and Langmuir isotherm. This indicated that Mg(OH) 2 seeds adsorption was monolayer chemical adsorption driven by electric attraction between positively charged Mg(OH) 2 seeds and -COO − ions on the cotton fiber surface. The X-ray diffraction (XRD) and SEM characterizations of the Mg(OH) 2 thin films covered cotton fabrics found that standing flaky Mg(OH) 2 crystals formed a shell of porous but continuous network on cotton fabric surface. Owing to the Mg(OH) 2 thin film covering, the fabric had fireproof property, lower thermal conductivity and higher optical absorbance in the UV, Vis and IR regions.