Organosolvent delignification of wood in the lower alcohols media is one of the promising methods for lignocellulosic biomass processing. The organosolvent lignins obtained do not contain sulfur and ash, and therefore are a promising raw material for processing into valuable chemical products. To study the structure of lignins, a large range of physicochemical methods is used. In this review, attention is focused on the methods of studying the structure and properties of organosolviable lignins, which have recently been greatly developed - gel permeation chromatography and thermal analysis methods. Examples of the use of these methods to study the molecular mass characteristics of organosolv lignins and their thermochemical properties are considered.