Effects of temperature and photoperiod on vegetative and reproductive growth were investigated in everbearing strawberry (Fragaria x ananassa Duch. cv. 'Summerberry') plants. At first, the plants were grown under 8- and 24-hr photoperiods at day/night temperatures of 20/15°C 25/20°C and 30/25°C for 16 weeks. At 20/15 and 25/20°C flowering continued under both photoperiods during the experiment although the number of inflorescences was larger under the 24-hr photoperiod. At 30/25°C, inflorescence formation was stopped under the 8-hr treatment and remarkably promoted under the 24-hr photoperiod. Vegetative growth was the most active at 20/15°C under the 24-hr photoperiod and it was seriously inhibited at 30/25°C by the 24-hr treatment. Secondly, 'Summerberry' plants were grown at 30/25°C under 8-, 10-, 12-, 16-, 20- and 24-hr photoperiods. Inflorescences of plants ceased to develop under 8 to 12-hr photoperiods. On the contrary, the development of inflorescences was promoted under 16 to 24-hr photoperiods. Vegetative growth was better under 8 to 12-hr compared with longer photoperiods. Furthermore, the plants were grown at 30/25°C under 11-, 12-, 13-, 14-, 15- and 16-hr photoperiods. Development of inflorescences was inhibited by 11 to 13-hr treatments and it was promoted under 14-hr and longer photoperiods. These results indicate that a critical photoperiod for the development of inflorescences of 'Summerberry' plants exists between 13- and 14-hr. Besides flowering behavior observed in the present study suggests that photoperiod affects on reproductive growth quantitatively.