Optical gain in quantum wire (QWI) lasers are theoretically investigated as functions of wire crystallographic direction taking valence band anisotropy into account. Calculations for GaAs cylindrical QWI with infinite barriers are performed by using the 4×4 Luttinger–Kohn Hamiltonian. Considering the structural optimization of QWI lasers from the viewpoint of crystallographic direction, we find that a [111]‐QWI lasers is the most suitable low‐threshold laser and that a [1,−1,0]‐QWI laser on a (110) substrate is the most suitable polarization‐stab‐ilized vertical‐cavity surface‐emitting laser. ©1996 American Institute of Physics.