The applicability of bremsstrahlung counting to in-situ measurements of high level tritiated water has been examined. A specially designed metallic vial fitted with a gold-coated beryllium window was prepared for the present examinations. Only tritiated water of a given amount was put into the vial. The volume dependence of the X-ray intensity showed that 5 cm3 of tritiated water is sufficient for measurements. It was found that the spectrum of X-rays induced by -rays consisted of only bremsstrahlung. The bremsstrahlung spectrum could be reproduced quite well by computational simulation. A good linear relation between the X-ray intensity and tritium concentration was obtained in the concentration range of 4 × 10-3-40 MBq cm-3. Furthermore, effect of nickel added as a model impurity to tritiated water was examined, and it was found that the tritium concentration can be evaluated from the X-ray intensity without any correction in the presence of impurity below 200 ppm.