MicroRNAs have been shown to be able to modulate the tumor microenvironment and the immune response and hence could be interesting biomarkers and therapeutic targets in immuno-oncology, however, dedicated analysis tools are missing. Here we present a user-friendly web platform MIO and a Python toolkit miopy integrating various methods for visualization and analysis of provided or custom bulk microRNA and gene expression data. We include regularized regression and survival analysis and provide information of forty microRNA target prediction tools as well as a collection of curated immune related gene and microRNA signatures and processed TCGA data including estimations of infiltrated immune cells and the immunophenoscore. The integration of several machine learning methods enable the selection of prognostic and predictive microRNAs and gene interaction network biomarkers. https://mio.icbi.at, https://github.com/icbi-lab/mio, https://github.com/icbi-lab/miopy. Supplementary data are available at Bioinformatics online. © The Author(s) 2022. Published by Oxford University Press.