Abstract This dataset contains the Sordelli collection of the Herbarium of the University of Milan. Specimens (exsiccata) were collected between 1851 and 1911 in Milan and its province and in Como lowland. Dataset content The dataset is composed by 5686 images in JPEG format. Their dimensions are 6000x4000 pixels and the resolution is about 305 DPI. For further information about image acquisition and digitization, please refer to the publication below. The dataset has been divided into 14 ZIP archives sized 4GB each approx, but the last one. The whole dataset is almost 52 GB. A subset made of 20 random images is provided as example material in the file "example_copies.zip". Both the main dataset and the example subset are provided with CSV files containing details about specimens. Terms of use The dataset is open access for scientific research and non-commercial purposes. The authors require to acknowledge their work and, in case of scientific publication, to cite the following paper: Baratè, A., Caccianiga, M., Caporali, E., Ludovico, L.A., Pinto, S., Presti, G., Sala, E., Testa, A.: Preserving and Promoting the Herbarium of the University of Milan through Digital Technologies. In: Proceedings of Florence HeriTech 2020, IOP Conference Series: Materials Science and Engineering, vol. 949, pp. 012066-1–012066-9. IOP (2020). ISSN: 1757-899X (online), 1757-8981 (print)