Carbon nanospheres of uniform diameter around 40 nm have been achieved in the absence of catalyst by microwave pyrolysis chemical vapor deposition. The products have been characterized by field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The results show that the nanospheres with high purity, which are solid by their cross-sections, consisting of concentric incompletely closed graphitic layers. Their thermal stability in dynamic air atmosphere is also discussed.