The aim of this study was to determine the optimum level of carbon dioxide to maximize the quality and yields of strawberries cultivated in a greenhouse. Specifically, two strawberry cultivars, namely, ‘Seolhyang’ and ‘Maehyang’, were subjected to varying concentrations of carbon dioxide and patterns linked to their productivity were noted. Both cultivars showed improvements across various physical variables (i.e., leaf area, crown diameter, plant height, fresh weight, and dry weight) when carbon dioxide concentrations were at 1,500 ppm. The optimum carbon dioxide concentration for increased fruit yields and quality was 1,000 ppm. When carbon dioxide was at 1,000 ppm the yields of ‘Seolhyang’ and ‘Maehyang’ increased by 1.99 and 1.78 times, respectively, compared to control plants. The influence of carbon dioxide on fruit color was negligible. However, the carbon dioxide increased the sugar content and sugar-acid ratio of the experimental fruits compared to control plants. Specifically, the sugar-acid ratio, which is directly related to taste, was at its highest when the concentration of carbon dioxide was at 1,000 ppm (i.e., for both ‘Seolhyang’ and ‘Maehyang’). Overall, the application of carbon dioxide culminated in improved yields and fruit quality for both cultivars of interest.