The surface structures obtained by scanning tunneling microscopy studies of two commercial glassy carbon samples, heat treated at 1000 and 2500-degrees-C, respectively, are presented and discussed. These glassy carbons consist of large areas of featureless amorphous regions which coexist with different types of ordered zones. In the glassy carbon treated at 1000-degrees-C, three types of microcrystallites have been observed : a hexagonal "graphitelike" structure with apparent interatomic distances di=2.2+/-0.1 angstrom, a structure in form of atom rows distant of 3.6+/-0.2 angstrom and a rectangular structure with a periodicity equal to 3.3+/-0.2 and 2.50+/-0.15 angstrom. In the glassy carbon treated at 2500-degrees-C three types of microcrystallites have also been observed : a graphitelike structure with d(i)=2.2+/-0.1 angstrom, a hexagonal "graphitic" structure with 2.5+/-0.15 angstrom, and a centered rectangular structure (a=6.8+/-0.4 angstrom, b=2.3+/-0.2 angstrom).