The progress of mechanization in forest harvesting is one of the factors that contributed to boost the competitiveness indices of the economic activity of forest production in Brazil. However, the use of mechanized harvesting systems in areas with steep slopes is still a technological challenge to forest companies, in particular in extraction operations. This study aimed to evaluate technically the forest extraction in mountainous terrains using a Forwarder with traction aid winch (TAW). Data were collected from an unprecedented operational test, performed in areas of Eucalyptus spp. in São Paulo state, Brazil. The various productivities of the Forwarder were evaluated in different extraction distances (ED), slopes, and with the use or not of the TAW. The results show that the Forwarder was efficient, and performed the extraction within acceptable limits of productivity. However, using the TAW on an increased slope led to a decrease in its productivity. It was concluded that the use of TAW and the increase in the slope decrease the productivity of the Forwarder, due to the fact that it takes more time to carry out the operational cycle elements on slopes above 25.1º where the loading was the operational cycle element that spent more time on any slope.