The critical behavior of La0.8Na0.2MnO3-Δ nanopowders at the paramagnetic to ferromagnetic phase transition is studied. The optimized critical exponents, through an iterative program based on Kouvel–Fisher method, were found to be as: ; . These obtained critical exponents does not match with the conventional universality classes. In addition, these and values are close the ones predicted by the mean-filed theory ( and ). It has been approved that the estimated critical temperature and the critical exponents are unambiguous and intrinsic to the La0.8Na0.2MnO3-Δ nanopowders. Based on the combination of the Landau model and the Arrott–Noakes equation, the isothermal magnetization curves and the magnetocaloric effect have been successfully simulated.