We investigate the impact of accounting for interactive plant phenology on the simulation of the June and August 2003 European heat waves. A sensitivity analysis is conducted here by using the WRF atmospheric model and the ORCHIDEE land-surface model over France with (1) a prescribed vegetation corresponding to year 2002 and (2) a dynamical vegetation model which leaves the vegetation freely evolving. It has been found that, accounting for the phenology dynamics has opposite effects on both events, it damps the temperature anomaly in June, while it amplifies the temperature anomaly in August.The evolution of leaf area index in the two simulations reveals the early and fast development of agricultural vegetation in the simulation with freely evolving vegetation. The vegetation also decays earlier in 2003 than during normal years. This behavior has two consequences. In June, the larger foliage development, caused by higher springtime insolation, contributes to enhanced evapotranspiration and therefore land surface cooling which limit the temperature anomaly during the heat wave. This effect is not as visible in mountainous regions where the presence of forest and the absence of agriculture do not lead to the same modulation of the local water cycle. In August, the early leave fall and the critical soil moisture stress contribute to largely suppress evapotranspiration and to enhance sensible heat flux thus amplifying the temperature anomaly. The modulation of the temperature anomaly caused by the effect of interactive vegetation phenology can reach 1.5°C for an average total anomaly of about 8°C (i.e. 20%).