La 1- xSr xMnO 3 nanoparticles were prepared by calcination of a molecular sieve MCM-41 soaked in precursor solution. Magnetic properties have been investigated by the magnetization measurements. Superparamagnetic behavior of the nanoparticles is observed both for the antiferromagnetic and ferromagnetic phases at low temperatures. For the antiferromagnetic phase, the superparamagnetic moment corresponds to the uncompensated moments in the antiferromagnetic particles. While for the superparamagnetism for the ferromagnetic phase is smaller than the superparamagnetism estimated for the single-domain ferromagnetic particles.