Dissolved and residual pine kraft lignin samples were isolated from different delignification phases of kraft flow–through cooks. The molecular weight distributions (MWDs) were studied by size exclusion chromatography using lithium chloride/N,N-dimethylacetamide (LiCl/DMAc), not previously applied to isolated softwood lignin samples before. The MWDs were compared with results obtained using tetrahydrofuran (THF) or lithium chloride/N,N–dimethylformamide (LiCl/DMF) as mobile phase. Some important characteristics of the isolated lignin samples including the MWDs are reported and compared with a previous study on birch wood kraft lignins.