We have investigated the luminescence of a series of M5 Eu(WO4)4-x (MoO4)x (M=Li, Na, K) phosphors and discovered that Na5 Eu(WO4)4-x (MoO4)x (0x4.0) exhibit the most intense red emission among the three investigated. Powder X-ray diffraction investigations show that a complete solid solution can be formed in the indicated composition range. The effect of chemical compositions on the luminescence properties of Na5 Eu(WO4)4-x (MoO4)x has been investigated and discussed. The Commission International de l'Eclairage chromaticity coordinates were found to be (0.66,0.33) for Na5 Eu(WO4)4-x (MoO4)x, which reaches the same level as that of the Y2 O2 S: Eu3+ commodity. The color-rendering index (R a) of a typical white-light-light emitting diode (WL-LED) based on Na5 Eu(WO4)2 (MoO4)2 was found to be 82.3, higher than that (i.e., Ra∼70.8) obtained for the WL-LED fabricated using the commodity of La2 O2 S: Eu3+ when the WL-LEDs were operated at a forward-bias current (If) of 20 mA at room temperature. Na5 Eu(WO4)4-x (MoO4)x is therefore suggested to be a potential red-emitting phosphor for WL-LED.