The growth of saturable absorber Cr 4+∶YAG crystals by liquid phase epitaxy (LPE) is reported. The absorption characteristics of this co-doped Cr,Ca∶YAG epilayer is analyzed. The transmission variation ΔT (i.e. the difference between saturated and unsaturated transmissions at 1.06 μm) could be adjusted easily in a range of 5%～30% by adjusting the concentration of Cr and /or the thickness of the epilayer during LPE and or by polishing. It is believed that this Cr,Ca∶YAG epilayer is well qualified for the development of passively Q-switched monolithic microchip laser as a solid-state saturable absorber. It shows that there is also the existence of Cr5+ ion in this Cr,Ca:YAG epilayer.