To evaluate debris flow downhill movements, it is necessary a rheological approach through constitutive modelling the descendent moving mass. Bingham s model is widely employed in the debris flow literature, its input parameters being plastic viscosity and yield stress. Such analysis provides understandings of the propagation of the debris motion in the field, once it provides an estimate of its velocity, thickness and range area. The present study presents a proposal for the assessment of soil yield stress and plastic viscosity, by laboratorial testing on a cylindrical tube slump test. Through the definition of shearing rates in the slump tests, yield stress and viscosity were determined on a plate–plate rheometer. Two natural soils from Rio de Janeiro, Brazil, with differing grain size distribution and plasticity, were used in the investigation. The experimental results obtained are compared with analytical and semi empirical solutions from the literature, and show that care must be taken in defining viscosities based only on data related to grain size. Correlations were obtained concerning to soil moisture and shear rates, defined in the slump tests, and also between plastic viscosity and yield stress, defined in the rheometer tests. As a result, good relationships between water content and both yield stress and viscosity were established. Comparing the obtained data with other results available in the literature it is concluded that the developed experimental methodology may provide a simple way to evaluate rheological parameters of soils for debris flow analyses.