The degradation of proteins by the 26S proteasome is initiated by protein polyubiquitination mediated by a three-step cascade. The specific ubiquitination of different target proteins is mediated by different classes of E3 ubiquitin ligases, among which the best known are Skp1-Cullin-F-box complexes. Whereas protists, fungi and some vertebrates have a single SKP1 gene, many animal and plant species possess multiple SKP1 homologues. In this paper, we report on the structure, phylogeny and expression of the complete set of rice SKP1 genes (OSKs, Oryza sativa SKP1-like genes). Our analyses indicated that OSK1 and OSK20 belong to a class of SKP1 genes that contain one intron at a conserved position and are highly expressed. In addition, our yeast two-hybrid results revealed that OSK proteins display a differing ability to interact with F-box proteins. However, OSK1 and OSK20 seemed to interact with most of the nine F-box proteins tested. We suggest that rice OSK1 and OSK20 are likely to have functions similar to the Arabidopsis ASK1 and ASK2 genes.