Polyacrylonitrile copolymers with different molecular weights (Mws) are synthesised by aqueous free-radical redox polymerisation technique. Polyacrylonitrile (PAN) and lignin-blended solutions are prepared in dimethyl sulphoxide solvent by varying the polyacrylonitrile/lignin content. The effect of lignin addition to PAN copolymer having different weight-average Mws on the rheological properties is explored. Rheological measurements indicate that the solution viscosity reduces with the increase in the lignin content. The Cole-Cole plot or Han plot and Casson plot are used to characterise the solution homogeneity. The slope value of the plot suggests that the molecular-level homogeneity of the solution is not affected much by the addition of lignin. Thermal-induced gelation of concentrated solution has been rheologically investigated to avoid overheating of solution during the dissolution, storage and transportation for further wet spinning process.