The distinction between tumor and healthy tissue is highly important during an oncological surgery but can be challenging. Optical methods for precise in situ tumor demarcation would be helpful to guide surgery, and thus easy-to-use systems are of high demand. Here, we present a novel MEMS-based confocal laser scanning microscope, named LSC-Onco, for tumor demarcation in oncological surgery. The measurement head of the microscope exhibits a compact size of (11x17x40) cm3 and is intended for use in a clinical environment. It includes a commercially available apochromatic 20x microscope objective with a working distance of 1.0 mm. For a sample overview, a subminiature camera with a field of view of 500 μm in diameter together with a Koehler illumination unit is integrated. Furthermore, for image slicing a z-shifter with a long distance travel range of 2000 μm and 5 nm minimum step size is included. Beam-splitters, filters, micro-photomultiplier tubes and all necessary driving- and read-out electronics are integrated into the measurement head. The core component of the laser scanning microscope is a proprietary electrostatically driven dual-axis MEMS scanning mirror developed at the Fraunhofer IPMS. This device features a quasi-static axis, a second resonant axis and is equipped with an elliptical mirror plate. The system can operate in a dual wavelength mode with fiber-coupled diode lasers at 488 nm and 638 nm. Using the LSC-Onco microscope and fluorophore-coupled tumor-specific antibodies, we visualized tumor margins in human skin cancer specimens outside the body (ex vivo) as a proof-of-concept.