Cowpea is one of the most consumed annual legumes in the world, but, despite its economic importance, the crop has low productivity in the Northeast of Brazil, being related to the genotypes used, climatic factors, and soil quality. In this context, this study aimed to evaluate the physiological parameters of nine genotypes in different phenological stages, cultivated under rainfed conditions. The experiment was carried out in the area of cowpea multiplication, belonging to the Federal University of Ceará (UFC), using a completely randomized design in a 9x2 factorial scheme, referring to nine genotypes and two stages of development (vegetative and reproductive) with ten repetitions, totaling 90 experimental plots. The evaluation of gas exchange (photosynthesis, stomatal conductance, transpiration, Ci/Ca ratio, and water use efficiency) were performed in the vegetative and reproductive phases (30 and 60 days after sowing), using the infrared gas analyzer (IRGA). It was verified that the variables of photosynthesis, stomatal conductance, and transpiration presented higher values in the vegetative stage concerning the reproductive stage, standing out of genotypes CE693, CE701, and CE735. For variables, Ci/Ca ratio, and water use efficiency, the genotypes with the lowest mean values were CE390 and CE570. The genotypes CE693, CE701, and CE735, presented better stability in the physiological parameters in the two phenological stages, and this may favor the production of cowpea.