For the first time it is possible to observe the excitation of surface plasmons (SP) on thin titanium nitride (TIN) films. From angle- and wavelength-dependent reflection measurements the dielectric function of TiN, and thus the optical constants, were calculated. Therefore, the main aim of this work was the determination of the real and imaginary parts of the dielectric function epsilon(omega) and thus the dispersion relation of SP on TiN. This method is an alternative to the standard technique of ellipsometry for determination of the complex dielectric function.