In this study, to develop lightweight clothing for extremely cold conditions, concentration, time, temperature, and pH-dependent dyeing of silk fabrics using Fe2O3 nanoparticles is conducted, and the dyeing characteristics, surface properties, light fastness, and thermal-insulation functionality are evaluated. The dyeing results show a light red color and red yellowish stains at concentrations of 0.5, 5, 15, 25, and 50g/L, with no increase in dye uptake at 50g/L. Therefore, the optimal dyeing conditions are 60°C for 40 min under pH 5. The light fastness of the dyed fabric shows minimal color difference (1.77) even after exposure to a UV-C lamp for 900 hours, thus indicating high light fastness. SEM analysis shows Fe2O3 nanoparticles on the surface of the dyed fabric, with an increase in particle density at higher dye concentrations. Thermogram analysis of the dyed fabric on a 30°C hot plate shows that the thermal insulation of the fabric dyed with a concentration of 0.5g/L is better than that of untreated fabric, whereas the fabrics dyed with concentrations of 5, 15, and 25g/L exhibit improved thermal insulation compared with that dyed with 0.5g/L. The fabrics dyed with concentrations of 5, 15, and 25g/L show similar thermal insulation properties. Therefore, silk fabrics dyed with Fe2O3 nanoparticles exhibit high thermal insulation and light fastness, thus rendering them suitable for use in combatant personal clothing.