It is highly desirable to red-shift the emission of Y3Al5O12:Ce 3+ phosphor in order to obtain a warmer correlated color temperature (CCT) in applications for blue light pumped white light emitting diodes (w-LEDs) with high color rendering index (CRI). In this paper, we reported the red-shifted emission of Y3MgSiAl3O12:Ce 3+ garnet phosphor for w-LEDs through a chemical unit co-substituting in solid solution design strategy. The fabrication temperature of the Y3MgSiAl3O12:Ce 3+ powder was optimized at 1600 ºC and its structure, photoluminescence properties, micromorphology, decay curves, quantum yield, as well as the thermal stability of the samples were investigated in details. The as-prepared Y3MgSiAl3O12:Ce 3+ phosphors displayed a broad excitation band ranging from 300 to 520 nm (centered at 450 nm), and presented an intense Ce 3+ 5d-4f emission band in the yellow light region (λem=564 nm, obviously red-shifted away from Y3Al5O12:Ce 3+). This can be explained by the increase of the crystal field splitting in the Ce 3+ 5d levels due to the chemical unit co-substitution of Al 3+ (I) and Al 3+ (II) ions by Mg 2+ and Si 4+ ions. The quantum yield of the Y2.92MgSiAl3O12:0.08Ce 3+ phosphor was measured as 61.8%. Further investigation on the packaged w-LEDs lamp by combining Y2.92MgSiAl3O12:0.08Ce 3+ phosphors on a blue InGaN chip exhibit a lower CCT and higher CRI compared to the commercial Y3Al5O12: Ce 3+ based device, indicating their outstanding strengths for potential applications in w-LEDs.