LaMnO$_3$ Nanoparticles systems were prepared by the sol-gel auto-combustion method, in order to analyze the structure and magnetic behavior presented by the compound prepared following a new alternative route of synthesis. Structural characterization, morphology and crystallite size was performed by X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy (TEM). The XRD study together with a Rietveld analysis showed that the LaMnO$_3$ compound crystallized in a perovskite hexagonal structure. The IR spectra showed that the compound has tensile energy bands in the Mn-O-Mn bonds related with the octahedron MnO$_6$; which are attributed to a characteristic vibration of the $ABO_3$ perovskite. An estimated size and morphological analysis was carried out by applying the Scherrer's formula and using Transmission Electron Microscopy (TEM), revealing non-spherical shape and particle sizes between 13~nm and 18~nm. The magnetic measurements $M(T)$ were performed by using zero-field-cooled (ZFC) and field-cooled (FC) protocols which revealed a positive Weiss temperature indicating the presence of ferromagnetic interactions with a Curie temperature, $T_C=150$~K.