Rice (Oryza sativa L.) yield is low under saline soil conditions due to the small number of spikelets per panicle (SN) and there are varietal differences in the sensitivity of SN to soil salinity. This study was carried out to determine whether varietal differences in the sensitivity were attributable to dry matter production under saline soil conditions. A sensitive variety IR28 and a tolerant variety IR4595-4-1-13 were grown in pots filled with sand and submerged in four saline solutions containing 25mM to 150mM sodium chloride (NaCl) from the later stage of spikelet initiation to the panicle emergence stage and compared to plants grown under low solar radiation (30% to 80% of natural radiation) . Control plants were grown without NaCl application under natural solar radiation. Under the saline conditions dry matter increase per shoot (ΔW) was more reduced in IR28 than in IR4595-4-1-13. The percentage of decrease of SN in IR28 was larger than that in IR4595-4-1-13, where the degeneration of spikelets on secondary rachis-branches was the main cause of the decrease of SN. The panicle dry weight at panicle emergence (Wp) was related to SN and the decrease of ΔW was responsible for the small Wp since dry matter distribution to the panicle (Wp/ΔW) did not change. There was almost no accumulation of sodium in panicle, but substantial accumulation was observed in leaf and stem, IR28 being a better accumulator. Under the low solar radiation conditions, though IR4595-4-1-13 maintained higher SN, there were small varietal differences in the response of ΔW, Wp and SN, while Wp/ΔW was enhanced due to the low solar radiation. Therefore, IR4595-4-1-13 was tolerant in terms of SN to soil salinity because a lower sodium concentration in leaves may maintain dry matter production, thus the limited changes in ΔW and Wp, resulting in a limited change in SN.