Stable ZnS/ZnO heterostructural nanoribbons are obtained via controlling the amount of O-2 during growth. The heterojunction is composed of single-crystal side-by-side nanoribbons of ZnS ([0001] direction) and ZnO ([11-2-1] direction). This work demonstrates the possibility of producing high-quality crystalline heterostructures at the nanoscale from two materials with a large lattice mismatch.