Phase matched noncollinear second harmonic generations (SHGs) are observed in 2‐methyl‐4‐nitroaniline (MNA) single‐crystal film waveguides. The phase matching condition is obtained by the cross point of the mode dispersion curves for the MNA waveguide. Theoretical analysis of the SHG conversion efficiency shows that the maximum efficiency is given by the conversion between the fundamental 1st mode and the SH 3rd mode. The experimental efficiency at this conversion is obtained to be 0.10% in the waveguide.