The development of a multichannel spectrometer based on single mode planar integrated optical waveguide and capable of measuring broad-band visible absorbance spectra of a weakly absorbing molecular blm at a solid-liquid interface is reported. The system was successfully tested by measuring spectra, over a 100 nn bandwidth, of a hydrated film of cytochrome c adsorbed to a glass waveguide surface. The approach should prove useful in spectral characterization of structure and function in thin film molecular assemblies at condensed phase interfaces.