Anthocyanins are widely common natural antioxidants and represent an important economic feature in vegetables, but the potential response of UVA–blue co-irradiation on the anthocyanin biosynthesis of pak choi is not clear. Here, we investigated the effects of the supplement of four doses of UVA to blue light on growth, metabolites and the anthocyanin biosynthesis of two cultivars of pak choi. The results revealed that supplementing UVA light to blue light positively affected the growth of the

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... k choi and elevated the soluble protein content and antioxidant capacity. Especially, when compared with a monochromatic blue light, the anthocyanin synthesis was enhanced with an increase in UVA light strength, which reached a peak value at the strength of 10 μmol·m−2·s−1. Further study revealed that the UVA–blue co-irradiation enhanced the transcription of partial light-induced and anthocyanin structural genes. The intraspecific difference in the expression patterns of MYB1 and PAP1 were observed in these two tested cultivars. MYB1 was significantly up-regulated in red-leaf pak choi, but down-regulated in purple-leaf pak choi. On the contrary, PAP1 was significantly up-regulated in purple-leaf pak choi, but down-regulated in red-leaf pak choi. To sum up, this study established an efficient pre-harvest lighting strategy to elevate the economic value of pak choi.