Liquid beam desorption mass spectrometry (LBD‐MS) is a powerful technique to isolate charged molecular aggregates directly from liquid solution (e.g., water) and to analyze them with sensitive mass spectrometry. A recent variant of the technique uses high‐pressure liquid chromatography valves for local liquid injections in the liquid carrier beam, which enables low analyte consumption and high‐speed sample analysis. A decisive and interesting feature of the technique is its linear response for proteins as well as small molecules such as amino acids over at least 3 to 4 orders of magnitude of liquid concentrations. In the present study, we highlight the application of LBD‐MS for the direct, fast, and quantitative analysis of bovine serum albumin (BSA) in nonpathogenic bovine serum solution without the need for internal standards and large sample preparation. From an evaluation of the peak intensities and with a calibration curve, typical concentrations of 5.2 · 10−4 mol · L−1 (estimated error <10%) for the undiluted samples have been determined, which is in good agreement with typical concentration of BSA in blood serum of healthy animals, as published in the literature.