<p>In this work, we investigate in detail the magnetic properties and magnetocaloric effect of a triple-layer polyphenylene dendrimer with mixed spins (1/2, 1, 3/2) using Monte Carlo simulations based on the Metropolis algorithm within the Ising model framework. Additionally, the ground-state phase diagrams are systematically established in several planes to identify the stable magnetic configurations at zero reduced temperature. Our analysis shows that the reduced critical temperature is influenced by the reduced exchange couplings Rqq and Rσσ. We have also discussed the influence of the reduced exchange couplings and the reduced temperature on the total magnetization of the system. Moreover, the magnetic hysteresis cycle is established. Further, we investigate the effects of the reduced external magnetic fields (h/Jss) on the specific heat (C_m), thermal magnetization (dM/dT), internal energy, magnetic entropy changes (-ΔS), adiabatic temperature changes (ΔT_a), and relative cooling power (RCP). The relative cooling power increases almost linearly with the reduced external magnetic field, indicating promising magnetocaloric performance. These results suggest potential applications in the design of nanotechnology devices and the development of refrigeration systems.</p>