In this study, we aim to investigate the photosynthetic adaptation of henna plants to various irrigation regimes and describe the effects of water stress on their growth performance and chlorophyll contents. For this reason, an experiment of four months was conducted. Henna plants were first grown in a greenhouse and then, exposed to three different irrigation regimes, whereby, they were irrigated up to the field capacity (FC) of 0% (control, T0), 50% of the control (moderate stress, T1) and 25% of the control (severe stress, T2). Results showed that exposure to drought induced an important decrease in gas exchange and photosynthetic pigment contents as compared to control. These shifts became more pronounced under severe stress (T2). Furthermore, after two harvests made, stomatal conductance and photosynthetic assimilation rates were significantly reduced under T2 conditions. In addition, a decline in total Chlorophyll amount and shoot dry weight was noticed, whereas, increases in the intrinsic water use efficiency and in the root-shoot ratio were discerned, especially, under the severe drought. These results revealed a close relationship between henna plants and irrigation dose and showed that for photosynthesis process and growth performance, the most appropriate water regime was the moderate stress (T1) rather than the severe stress (T2).