To promote the sustainable development of the Amazon region, we are confronted with a lack of knowledge concerning small-scale farming on pioneer fronts. Current knowledge leads us to believe that work organization is relevant for the sustainability and transformation of these farms. Taking as an example dairy-beef cattle farms in Uruara (Para), this paper aims to produce knowledge on farmers' labour with the view of guiding future research and development actions. The farms are extensive grassland systems, with low levels of inputs, equipment and technology. Most of the tasks (milking, grazing management) are performed manually. A study, based on the quantification of working time shows that most of the activities (milking, pasture management) are carried out exclusively by the family manpower, helped sometimes by wage earners, volunteer workers and farmers' mutual aid. The study reveals the high variability of routine work (from 913 to 3,955 hours per year for milk production) and seasonal work (from 17 to 328 days per year). In order to manage their cattle and pastures, farmers' technical strategies are also very different (time reduction of labour, control and reduction of the peak work period, modification of ,manpower). The analysis of their trajectories clearly proves the alterations of the interactions between agricultural and non-agricultural activities, cattle production and working groups. Our contribution confirms that labour organization must be taken into account to support sustainable changes of these dairy-beef livestock farms. A better organization of work would facilitate the adoption of new techniques and practices. An aim is to investigate ways to rationalize these farmers' labour, which is characterized by diversified situations. Actions of research should be approached through multidisciplinary point of views.