A new micro molecular tagging velocimetry (μMTV) setup has been developed to analyze velocity fields in confined internal gas flows. MTV is a little-intrusive velocimetry technique. It relies on the properties of molecular tracers which can experience relatively long lifetime luminescence once excited by a laser beam with an appropriate wavelength. The technique has been validated for acetone seeded flows of argon inside a 1 mm depth rectangular minichannel, with a multilayer design offering two optical accesses. Velocity profiles have been obtained using a specific data reduction process, with a resolution in the order of 15 μm. The experimental data are compared to theoretical velocity profiles of compressible pressure-driven flows. A good agreement is observed, except close to the walls, where the accuracy would still need to be improved. Following these first results obtained at atmospheric pressure, the influence of pressure on the luminescence intensity of acetone molecules is analyzed. The obtained data lead to a discussion of MTV applicability to rarefied flows and its possible use for a direct measurement of velocity slip at the channel walls.