Abstract: Liangyoupeijiu is a two-parental-line, and Shanyou63 is a three-parental-line hybrid rice (Oryza sativa L.). Although both belong to the indica subspecies, they have obvious differences with respect to morphology, physiology and grain quality. Variations in endosperm protein compositions were studied by comparing the 2-D electrophoresis (2-DE) maps for these two cultivars of hybrid rice. After matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS) analysis, a 21-kDa precursor of 19-kDa globulin was identified as the major storage protein for both cultivars. Some isoforms of peroxiredoxin and seed maturation protein were found to only exist in Shanyou63, whereas aldose reductase and starch granule-bound starch synthase were only detected in Liangyoupeijiu. These data might provide a foundation for further comparative studies of these two cultivars of hybrid rice.（*Author for correspondence. Tel: +86 (0)10 6283 6545; Fax: +86 (0)10 6259 6594; E-mail: shshen@ibcas.ac.cn）

Key words: endosperm, hybrid rice, mass spectrometry, matrix assisted laser desorption/ionization time of flight, 2-D electrophoresis.