The Southeast Region of Brazil, which is affected by the South Atlantic Convergence Zone during the summer, and by frontal systems in the winter, has the lowest rainfall predictability of the country, seen in results of the AGCM CPTEC/COLA. This is a transition region, between the tropical regime to the north (Nordeste), which has high predictability, and the extratropical regime to the south, which has medium predictability. The monthly model results indicate an average of the daily conditions during the period, and most of the precipitation anomalies in this region is associated to the behaviour and intensity of frontal systems that are simulated by the model. In this study, the number of frontal systems which affects southeast Brazil, their behaviour and the large scale atmosphere characteristics, are analysed in daily AGCM CPTEC/COLA model results of nine integrations, in a ten years simulation. It is noticed that the model reproduces the characteristics and evolution of the frontal systems over southeast Brazil, when the analysis is performed for each individual integration, but the intensity of atmospheric changes is subestimated by the model. Composite of cases for each season reproduce the low level wind confluence, troughs at upper level and typical pressure and geopotential fields. However, when the ensemble mean is analysed, the typical features are not displayed, because of the large dispersion among members in the analysed region. The interannual and seasonal variability of frontal systems behaviour and atmospheric characteristics simulated by the model will be also shown.