One of the major challenges in nowadays particle physics and astrophysics is the determination of the absolute neutrino mass scale. A powerful tool to evaluate the effective neutrino mass is the calorimetric measurement of the energy released in a nuclear decay involving neutrino. In order to reach a sensitivity on the neutrino mass of the order of 1 eV, not only detectors characterized by high performances (i.e. energy and time resolution of ∼ eV at keV and ∼ 1 μ s, respectively) are needed but also many detectors working in parallel are required. Microwave frequency readout provides an effective technique to read out large arrays of low temperature detectors allowing to reach a multiplex factor of the order of thousands. This technique is the one used to read out the 1000 Transition Edge Sensors of HOLMES, an experiment that aims at measuring the electron neutrino mass by means of the electron capture (EC) decay of ¹⁶³Ho with an expected sensitivity of the order of 1 eV. In this contribution we present the characterization of the microwave-multiplexed readout system, and the results obtained with the detectors specifically designed for HOLMES.