Аннотация:This work presents some preliminary results of using oxygen isotopes ratio (δ18O) for diagnostics of transient layer of upper permafrost of the coastal plains of Eastern Chukotka, NE Russia. Study methods included drilling of active layer and transition zone of permafrost and stable core isotope ratios analysis. The study revealed that δ18O values of ice from transient layer ranges from –11.5‰ to –14‰. These values differ from those for massive ice beds and ice wedges in this region that allowed us to use stable isotope ratio as a diagnostic criteria of transient layer. The distribution of δ18O values with depth is associated with the migration with light isotopes downsection and freeze-thaw processes. The results can be used for assessment of transient layer spatial distribution using shallow drilling and distinguishing it from massive ice bodies.