In this study, the morphology of zinc sulfide (ZnS) produced on carbon nanotubes (CNTs) by heat treatment was investigated. It was found that ZnS nanocrystals were formed on the outermost shells of CNTs in the shapes of ultrathin films, quantum dots, and nanorods. X-ray diffraction patterns show synthesized ZnS has the wurtzite structure. Hexagonal cross sections of some ZnS nanorods prove that they were grown along the <0 0 0 1> direction on the surface of CNTs. ZnS nanorods were synthesized without using any catalyst differently from the previous reports. Heterojunctions between CNTs by these ZnS nanocrystals were also. found, which can be applied for nanosized optic and optoelectronic devices. (C) 2003 Elsevier Science B.V. All rights reserved.