To study the light-induced expression mechanism and the transport of the nascent polypeptide into the chloroplast, a cDNA clone and a genomic clone of the small subunit of ribulose 1,5-bisphosphate carboxylase (rbcS) was isolated. A cDNA library was constructed with mRNA isolated from the leaves of rice seedling grown in the light. A cDNA clone was isolated by differential screening with radiolabeled cDNA prepared from mRNA of the leaves of rice seedling grown in the light or dark. A rice genomic DNA library was constructed in pUC18 vector with rice total DNA isolated from rice leaves. A genomic clone Grbcs 2.5 was isolated from the library and restriction enzyme mapping was carried out by Southern blot analysis with cDNA clone. The structure of Grbcs 2.5 was determined by nucleotide sequencing. It consists of 2 exons and 1 intron, spanning over 630 bp and encode 175 amino acids. Comparison of the nucleotides and deduced amino acids to other rice Rbcs shows close homologies.