Platinum nanoparticles were electrocrystallized on amorphous carbon film and on sol-gel modified carbon film deposited on gold mesh grids. These Pt-modified surfaces were characterized by transmission electron microscopy and energy dispersive spectroscopy. Particles deposited on bare carbon surfaces exhibited polytetrahedral crystallographic morphology. Meanwhile, laterally dendritic growth of platinum formed by aggregation of primary particles (3-5 nm) were found on the sol-gel modified carbon surfaces. This is a new kind of morphology for electrodeposited platinum with a high specific and accessible surface area, holding great promise for Pt-catalyzed reactions. The characterization gives direct information on the microstructures of electrochemically produced particles, facilitating function and structure-correlating studies.