Positively charged CdS nanoparticles having diameter of 3.0 ± 0.2 nm were prepared by the chemical modification of their surfaces with thiocholine. Chains of size-quantized CdS nanoparticles were prepared by using the electrostatic interaction between positively charged nanoparticle surfaces and the phosphate groups of DNA molecules. The observation by transmission electron microscopy revealed that the CdS nanoparticles were arranged in a quasi one dimension with dense packing. The line width of a nanoparticle array was equal to the diameter of CdS nanoparticles that was ca. 3.0 nm. The average distance between the centers of the adjacent nanoparticles was estimated to be 3.5 nm, which was almost equal to the length of 10 base pairs in DNA double strands.