The effect of temperature and solvent isotopic composition on the position of absorption maximum and width of the absorption band in UV-Vis spectrum of ascorbate, predominant reactive form of vitamin C in physiological conditions, has been studied in this diploma thesis. The UV-Vis spectra of 5∙10-5 mol/dm3 ascorbate solutions in H2O and D2O in the temperature range from 1 to 55 ºC have been measured by using three different spectrophotometers with previously determined measuring characteristics. By measuring the UV spectrum of ascorbate solution ranging from 5∙10-3 to 5∙10-5 mol/dm3, it was found that the position of the absorption band maximum is not dependent on the concentration of ascorbate. From the UV spectra obtained in H2O and D2O, it has been shown that increasing the temperature increases the absorption band width and shifts the absorption maximum to higher wavelenghts. These changes are 1.2 nm for the of absorption band width and 1.1 nm for the absorption maximum position in the temperature range of 50 ºC. Differences in the UV-Vis spectra of the ascorbate solution in H2O and in D2O were also found. The absorption maximum position in UV-Vis spectrum of the ascorbate solution in D2O was shifted by 0.7 nm at lower wavelenghts, and the width of the absorption band was 0.8 nm less than the UV-Vis spectrum of ascorbate solution in H2O at the same temperature. The spinlattice relaxation times (T1) measured by NMR spectrometer for 1H ascorbate nuclei in 10 % D2O + 90 % H2O solvent are about the three times shorter than the corresponding T1 for 1H nuclei in 99 % D2O. The obtained results has been interpreted by solvation changes, or by the ascorbate vibrational and electronic states energy changes resulted as a consequence of slowing down the solvent and ascorbate hydrogen bonds reorganization in a solution caused by lowering the temperature or isotopic substitution. Since these changes include the π orbital involved also in charge transfer reactions, these changes may be related also to the ascorbate reactivity what could be useful in research of charge transfer reactions involving ascorbate in complex processes which take place in biological systems.