In the present work we developed a sample preparation approach for the combined bottom-up and top-down proteomics analysis of small open reading frame encoded proteins (SEP). Key improvements were made by the application of solid phase extraction (SPE) supported enrichment of LMW proteins, followed by two-dimensional LC-MS top-down analysis encompassing both HCD and EThcD ion activation. Bottom-up experiments were used to support and confirm top-down data interpretation. This strategy allowed for the top-down characterisation 36 proteoforms mapping to 12 SEP of the archaea Methanosarcina mazei, and for the first time the identification of posttranslational modifications in these microproteins.