Gross primary production (GPP) is the important measure of the net ecosystem exchange of CO2 between the atmosphere and terrestrial ecosystems. In this study, the Vegetation Photosynthesis Model (VPM) was applied at Ratchaburi flux tower sites in an effort to evaluate the potential of GPP upscaling. A simulation of the VPM model was performed using indices derived from the MODIS 8-day composites, air temperature and PAR data collected at the Ratchaburi tower site during 2010-2011. To evaluate the model agreement, three statistics RMSE (root mean squared error), MAE (mean absolute error), and R2(coefficient of determination) values were used. In general, the validation of simulation results from 92 observation values during 2010-2011 showed that the predicted GPP agreed well with the observed GPP of dry dipterocarp forest with R2= 0.75, RMSE=2.34 umol.m-2, MAE=2.06 umol.m-2. This study demonstrated the potential of the VPM model for quantifying the seasonal dynamics and inter-annual variations of GPP of deciduous forest.