Abstract: Four cases of pigmented naevus and two cases of blue aaevus with typical clinical and histologic manifestations were observed under electron microscopy. There were many melanosomes which were mainly in the third and fourth stage with various sizes and shapes in the cytoplasms of the cells of pigmented aaevus. The melanocytes of the blue naevus containing a large number of the third and fourth stage melanosomes chiefly located in the deeper part of the dermis. The large spherical melano-bodies in pigmented naevus and blue naevus probably represented the degenerative phenomenon or they might be formed after the Iys osomes had swallowed the degenerative' products of the melanosomes. This paper also discussed the cause from which different coloui"s of naevi were found, Besides the deeper location of the melanocytes and the factor of refraction, the amount of the melanosomes within the melanocytes and pigmentation of the meIanosomes also played some roles.