Diuron is a widely used herbicide on pineapple cultivations. However, its application is recommended only for the implementation of the crop. The objective of this work was to evaluate the gas exchanges of four pineapple cultivars submitted to the application of the herbicide diuron at their reproductive stage. The experiment was conducted with the IAC Fantástico, Vitória, MD2 and Pérola pineapple cultivars using the active ingredient diuron at a dose of 7.5 mL L-1. Measurements of CO2 assimilation rate, stomatal conductance, transpiration, vapor pressure deficit and water use efficiency were carried out weekly, by the hour, on two plants per cultivar, over a 24 hour period. These determinations were carried out two days before the application of the herbicide and 8, 15, 22, 29 and 36 days after application of the herbicide. Measurement of photochemical efficiency was performed weekly on the same dates and all these determinations were made on the ‘D’ leaf. Measurements of gas exchange were performed with an infrared gas analyzer (IRGA) and of chlorophyll a fluorescence with a fluorometer. The application of diuron reduced the assimilation of CO2 in the pineapple varieties IAC Fantástico, Vitória, MD2 and Pérola, at their reproductive phase, in all CAM metabolism stages. Diuron promoted a temporary reduction of the stomatal conductance and a temporary increase in water use efficiency. The photochemical efficiency of the studied pineapple cultivars was negatively affected by the herbicide diuron, with the recovery of the initial values by cultivar IAC Fantástico.