June-bearing strawberries cannot be produced in summer because they require low temperatures and short days for flower bud formation, and because high air temperatures decrease fruit yield and quality. I tried to produce fruits of June-bearing strawberry in summer by controlling day length and air temperature. Seedlings of three cultivars, ‘Sachinoka’, ‘Benihoppe’, and ‘Marihime’, were transplanted to a greenhouse in autumn 2012 and grown in rockwool culture. In late spring 2014 the growing area was covered with shade cloth having heat-insulating properties. Day length was controlled to 12 h and the air was cooled initially to 28/15°C (initially) and then to 28/10°C in summer. In the control, air temperature was not cooled. In the air-conditioned area, the vapor pressure deficit was always lower and the CO2 concentration in the dark period was higher than in the control. In control plants, fruit yield after May was very low, and no fruit was harvested in September, while the air-conditioned plants produced similar yield as in winter. Soluble solids content and firmness of fruits in the air-conditioned area in summer were higher than in fruit harvested in winter.