The structural and magnetic properties of micrometer and nanometer-sized samples of La0.9Sr0.1MnO3 manganite have been studied, using powder X-ray diffraction (XRD), transmission electron microscope, field emission scanning electron microscope and magnetic measurements. The XRD refinement result indicates that both samples have rhombohedral structure. The micrometer-sized sample shows long-range ferromagnetic ordering with transition temperature, Tc ~ 225 K. In a contrary, the temperature dependence of Ac susceptibility of nanometer-sized sample shows broad peak which is frequency dependent. The result of Ac susceptibility data for nanometer-sized sample revealed super-spin glass behavior for this sample at low temperatures. Also, the Dc magnetization measurements confirmed the superparamgnetic behavior of nanometer-sized sample at room temperature.