UV-spectrophotometry data of technical lignin samples in solutions is made available here, which was acquired after ambient aging for up to 110 days in DMSO solvent or looped measurements on fresh solutions in DMSO or 0.2N NaOH in water. UV-spectrophotometry of lignin is a useful technique, as it can a) quantify the concentration and purity of lignin in a given sample, b) determine the abundance of phenolic hydroxyl groups, and c) yield qualitative information about chemical modification of the lignin macromolecule. In addition, the technique is rapid and easy to use. Still, solutions of lignin are known to be unstable; in particular at high pH or in presence of UV-light. The data in this article may hence serve as guide in the experimental conduct and design, as it shows the reproducibility of UV-spectrophotometry measurements of lignin.