Structural, electrical, and magnetic properties of La0.5Sr 0.5CoO3 nanoparticles prepared by sol-gel technique are investigated and the results reveal a size-induced metal insulator transition in the electrotransport behavior. The field cooled and zero field cooled magnetizations display a broad paramagnetic to ferromagnetic transition at Tc with a large magnetic irreversibility. Attempts are made to get an idea about the spin states in the nanoparticles. The observed frequency dependent shoulder in the in-phase (X′) component and the peak in the out of phase (X″) component of the ac susceptibility in the low temperature region indicate the glassy nature of the samples. © 2008 American Institute of Physics.