IR absorption spectra of urea, urine without any deviation in composition and kidney oxalate calculi are studied. The shifting of stretching vibrations of carbonyl group C=O confirms that assert that the joining of calcium oxalate molecules and oxalate complexes join to urea molecules via oxygen atom of urea. The shifting of COOsymmetric stretching vibration frequencies may testify the presence of molecules and aggregates of calcium oxalates. Obtained results may be useful in developing new methods in early diagnostics of different diseases.