Nanofiltration membranes with molecular weight cut-off around 200 Da were evaluated to concentrate anthocyanins and ellagitannins in a blackberry juice. Temperature was 30°C and cross-flow velocity 0.3 m/s. Transmembrane pressures varied from 0.5 to 3 MPa. At volumetric reduction ratio (VRR) of 1, higher transmembrane pressures caused an increase of permeate flux and of retention of total anthocyanins (>94%) and total soluble solids (44–97%). Every membrane presented 100% of total ellagitannin retention. Results were represented using the solution-diffusion model. NF270 membrane at 3 MPa showed the highest potential for concentration of blackberry's main polyphenolic compounds (highest permeate flux and solute retention). Nevertheless, a simulated increase of VRR showed that permeate flux declined as the concentration of the feed solution increased. NF270 membrane may also be of interest to deacidify the juice, since at high pressures, sugars were completely retained and retention of acids was under 90%.