Part of the C-terminal of rice phytochrome B was used as bait to screen a cDNA library constructed from young rice panicles in a yeast two-hybrid screening. A positive clone was selected, and the sequence was characterized as encoding a FKBP protein, which is a putative developmental regulator. An in vitro pull-down assay using recombinant proteins and analysis of bimolecular fluorescence com-plementation in onion epidermal cells indicated that two proteins interact in vitro and in vivo. The results of reverse transcription poly-merase chain reaction showed that two genes were co-expressed in the examined rice organs, suggesting that OsFKBP1 may play a role in light signal transduction in rice.