This experiment was conducted to investigate the effects of diurnal alternation of nutrient solution salinity on growth and fruit quality of tomatoes (Lycoperisicon esculentum cv. 'House momotaro') hydroponically grown in root intercept bag-NFT (RIB-NFT) system. Plant height was the lowest in the high concentration during daytime (6/1 dS m-1, day/night). Yield was very high in the concentration of 1/1 dS m-1, it decreased with increasing the concentration of nutrient Yield was higher at low concentration (4/1 dS m-1) at nighttime compared to the same concentration (4/4 dS m-1) at daytime and nighttime, and the reverse (1/4 dS m-1) was similar to the control (perlite culture). Yield was greatly reduced by higher concentration at daytime than nighttime, and the decrease was alleviated by lower concentration at nighttime. With increasing the concentration of nutrient solution during daytime, sugar content of tomato fruit was increased, but yield was decreased. In the other experiment, tomato plants were hydropoically cultured in NFT system diurnally alternated between Aichi's solution and Ca(NO3)2 solution. Ca(NO3)2 solution was supplied for 4 hours from 10:00 to 14:00 at daytime and from 22:00 to 2:00 at nighttime, respectively, and Aichi's solution was supplied for the time except the 4 hours. Ca content of leaves and sugar content of fruit were increased by supplying Ca(NO3)2 solution at daytime compared to nighttime, but plant growth was greatly suppressed by supplying Ca(NO3)2 solution with the concentration of 4 dS m-1(4/4Ca dS m-1) at nighttime.