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Off-season vegetable crops in a greenhouse need supplementary light intensity and CO2 concentration to obtain good growth and fruit quality. The objective of this study was to investigate the effects of supplementary light intensity and CO2 concentration on the photosynthesis, yield, and fruit quality of fresh hot pepper (cultivar Meite). Two light intensities-supplementary (SLI) and natural (NLI) light intensity with the averaged photosynthetic active radiation of the whole growth period of 463 and 233 mu mol m(-2) s(-1), respectively-and 4 CO2 concentrations (400, 550, 700, and 900 mu mol mol(-1)) were conducted on pepper planted in pots in phytotrons over the autumn and winter seasons in the arid Northwest region of China. Results showed that: (i) CO2 enrichment significantly increased the net photosynthetic rate (Pn), water use efficiency (WUE), yield parameters, and fruit storage qualities, but decreased the fruit nutrition qualities to different extents. (ii) SLI increased Pn, WUE, and fruit nutrition qualities to different extents, and increased fruit yield per plant (FYPP) by 157%. (iii) The treatment with SLI and a CO2 concentration of 550 mu mol mol(-1) can maximize the overall quality of pepper fruits and significantly increase FYPP with a first ranking in the technique for order of preference by similarity to the ideal solution (TOPSIS) method. Therefore, the yield of pepper grown in the off-season was increased and fruit quality was maintained by SLI and moderately increasing CO2 concentration (550 mu mol mol(-1)).