Abstract: Two amino-functionalized diatomite (DE) composites modified by 3-aminopropyltriethoxysilane (APTS) or glycine (GLY) (i.e., APTS/DE and GLY/DE) were successfully synthesized via the wet chemical method for the time- and cost-efficient removal of indoor formaldehyde (HCHO). First, the optimal preparation conditions of the two composites were determined, and then their microstructures and morphologies were characterized and analyzed. Batch HCHO adsorption experiments with the two types of amino-modified DE composites were also conducted to compare their adsorption properties. Experimental results indicated that the pseudo-second-order kinetic and Langmuir isotherm models could well describe the adsorption process, and the maximum adsorption capacities of APTS/DE and GLY/DE prepared under optimal conditions at 20°C were 5.83 and 1.14 mg·g⁻¹, respectively. The thermodynamic parameters of the composites indicated that the adsorption process was spontaneous and exothermic. The abundant amine groups grafted on the surface of DE were derived from the Schiff base reaction and were essential for the high-efficient adsorption performance toward HCHO.