We investigated the combined effects of night-break treatment performed three times per week and subsequent exposure to cold air by opening the greenhouse windows on the growth and quality of December-sown spinach (Spinacia oleracea L.). Plant height and fresh weight increased as a result of the night-break treatment, but plant elongation decreased because of the exposure to cold air. On comparing similar-sized harvests, the sugar concentration (Brix value) and L-ascorbic acid level were significantly higher but the nitrate (NO₃^-) level was lower in the combined treatment than in the control plants without the night break and exposure to cold air. These results suggest that the combined method of the night break and subsequent exposure to cold air would be effective to produce high-quality spinach without delaying the harvest.