In this article, we propose a facile method for synthesis of K2SiF6:Mn4+ phosphor and discuss its promising application in warm-white light emitting diodes (LED). The K2SiF6:Mn4+ was synthesized from SiO2 powders through redox reaction in HF/KMnO4 solution. The optical properties of LEDs containing different ratios of K2SiF6:Mn4+ phosphor and commercial Ce3+-doped garnets (YAG-40) yellow-green phosphor were studied. A warm-white LED, with color temperature of 3510K and color rendering index of 90.9 and efficacy of 81.56lm/W was demonstrated.