Taking the cucumber cultivar 'Jinyou 3' as test material, this paper studied the variations of the mRNA expression and activities of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), fructose-1, 6-bisphosphatase (FBPase), glyceraldehydes-3-phosphate dehydrogenase (GAPDH), fructose-1, 6-bisphosphate aldolase (FBA), and transketolase (TK) in cucumber seedling leaves under suboptimal temperature and low light intensity (ST+LL). In the treatment of ST+LL, the leaf area and the dry mass per plant decreased remarkably, compared with the control. On the early days of ST+LL treatment, the gene expression of Rubisco rbcL and rbcS, FBPase, GAPDH, FBA, and TK declined markedly, the activities of the enzymes except TK obviously weakened, and the photosynthetic rate (P(n)) decreased rapidly. 3 days later, the gene expression of Rubisco rbcL and rbcS and the initial activity of Rubisco showed a continuous decrease but the decrement was obviously lesser, the total activity of Rubisco and the activities and gene expression of FBPase, GAPDH, FBA, and TK had an increasing trend, and the P(n) ascended simultaneously. When the treating time exceeded 6 days, the gene expression and the activities of Rubisco and FBPase tended to be constant, while those of the other enzymes as well as the P(n) presented a decreasing trend. These results suggested that the decline of the gene expression and activities of the photosynthetic enzymes in cucumber seedlings under suboptimal temperature and low light intensity was the important reason which led to the decrease of P(n). The adaptation of photosynthetic apparatus in cucumber seedlings to suboptimal temperature and low light intensity was related to the activation mechanisms of photosynthetic enzymes.