A remote sensing method for assessing LAI index using airborne lidar data is proposed. A calculation body of the proposed method is based on regression model which couples LAI value and lidar data derivatives. Multiple regression equation is constructed. The results of experimental investigation confirm the effectiveness and high accuracy of the proposed method. The paper presents a review of the contemporary approaches to the assessment of leaf area index (LAI) as one of most comprehensive and objective indicators of photosynthesis processes activity of vegetation. Methods for LAI in-situ assessing, its procedures and instrumental support are described in brief. It is emphasized that the main and absolute advantage of in-situ methods is the reliability of calculated LAI estimates. However, the application of in-situ methods is connected with significant problems when it is necessary to assess photosynthesis processes activity level for vegetation in cases of vast areas with time limitations. As the authors observe, for similar cases is more promising to use remote sensing techniques and technologies. Directions for further research to improve the precision of the method are outlined therewith.