Light is very important for plant growth and a major limiting factor in indoor plant cultivation, such as in balconies. This study was conducted to investigate the light intensity and lettuce (Latuca sativa L.) growth in an apartment balcony affected by the direction of balcony. Photosynthetic photon flux (PPF), air temperature, and relative humidity in the east-, south-, or west-facing balcony were measured for a year. The lettuce was grown in the east-, south-, or west-facing balcony. The time and amount of light entering into the balcony differed according to the direction of the balcony window. Whereas light entered into the east-facing balcony from sunrise to noon, it entered into the west-facing balcony afternoon before sunset. The temperature and humidity in the balcony also varied according to the direction of the balcony window. Daily Light Integral (DLI) in the south-facing balcony was 20~50% of outdoor and DLI in east- or west-facing balconies was 10~20%. Also, the environmental characteristics of the balconies were affected seasonally. In the spring (from March to May), the DLI was around 10 mol･m-2･day-1 and the average temperature was around 25°C. But the DLI was below 10 mol･m-2･day-1 and the average temperature and relative humidity were around 30°C and over 60%, respectively, in the summer (from June to August). In the balcony, the average temperature was maintained around 10°C even in winter, which is a condition of freezing outdoor. Growth of the lettuce in the south-facing balcony was better than that of the other directions. This is attributed to better environmental conditions of south-facing balcony. Therefore, considering the environmental characteristics of the balcony, selection and management of crops with relatively low light demand like leafy vegetables are required. It is also recommended to cultivate crops from autumn to spring.