We have measured the third harmonic generation spectra of epitaxial chloro‐indium phthalocyanine (ClInPc) thin films. The χ(3) spectrum in the wavelength range of 970–1650 nm reveals resonance features of ClInPc. Theoretical analysis of the third‐order nonlinear optical channels in phthalocyanine allows the assignment of the observed resonances to three‐ and two‐photon resonances of χ(3).