Phase stability of pseudo-ternary (Ga,In,Mn)As and (Ga,In,Mn)N alloys with zinc blende (ZB) and rock salt (RS) structures is investigated by means of the first principles full-potential linearized augmented plane-wave method. Calculated results predict that the ordered and disordered states are less favorable with respect to the phase separation. However, the Mn solubility into ZB GaAs increase as the In composition increases. In addition, the Mn-doped GaAs with x(Mn) less than or similar to 0.44 (and GaN with x(Mn) less than or similar to 0.63) favors the ZB structure over the RS structure regardless the In incorporation. (C) 2011 Elsevier B.V. All rights reserved.