For selective laser sintering (SLS) the improvement of the processing condition is important for the mechanical, optical and surface properties of the final product. This includes the behavior of the used polymer powder in in the printing chamber and the material behavior during the sintering process. Polyamide 12 (PA12) powder is a widely used material for SLS. During the process, this powder is stored at temperatures just below the melting temperature in the printing chamber. After the sintering process, the remaining powder is recycled by mixing with fresh powder. Annealing at elevated temperatures below the melting range, PA12 is not chemically stable. Molecular growth occurs, this is connected to an increase of the melt viscosity. This influences the coalescence of the powder particles during the sintering process. For the improvement of the recycling process of PA12 powder a quick and simple method is required to measure variations of viscosity. Presented is a method using thermal mechanical analysis of the powder to measure a viscosity parameter. It is shown, that this parameter can characterize the influence of the thermal history on the processability of recycled PA12.