A study was carry out evaluating the latent heat flux or reference evapotranspiration (Etr) using the Penman- Monteith equation over a well- irrigated feccue. The perfomance of the Penmam- Monteith equation was evaluated usisng latent heat flux (or reference evapotranspiration) measured from the Bowen ratio energy balance method. Results indicate that the Penman - Monteith model with a variable canopy resistance was able to predict latent heat flux with standard deviation (DEE) of 19 W/m2 and an absolute error (Ea) of 5,4%. On daily basis DEE and Ea 0.42 mm/d and 3.0% respectively.