High-milk protein concentrates (>80%) are typically produced by ultrafiltration (UF) with constant-volume diafiltration (CVD). Polymeric spiral-wound (SW) UF membranes with a molecular weight cut-off (MWCO) of 10,000 Da are mostly used in dairy plants to maximize protein retention. Flux decline and membrane fouling during UF have been studied extensively and the selection of an optimal UF-CVD sequence is expected to have a considerable impact on both the process efficiency and the generated volumes of by-products. The objective of this work was to characterize performances of UF-CVD process in terms of permeate flux decline, fouling resistance, energy consumption and retentate composition as a function of MWCO (10,000 and 50,000 Da) and UF-CVD sequence (3.5×–2 diavolumes (DV) and 5×–0.8DV). UF-CVD experiments were performed on pasteurized skim milk by means of a pilot-scale filtration system (GEA NIRO) operated at 50°C and under a constant transmembrane pressure (TMP) of 465 kPa. Energy consumption was measured in situ for each UF-CVD sequence and was expressed as energy required to produce 1 kg of protein. Results showed that MWCO had no impact (P > 0.05) on permeate flux for a same UF-CVD sequence. However, permeate flux values were significantly higher during CVD for the 3.5×–2DV sequence whatever MWCO (P < 0.05), which could be explained by lower concentration polarization of milk components at the membrane surface when a larger DF volume was used. Regardless the MWCO, the 5×–0.8DV sequence showed a significant increase (P < 0.05) in energy consumption. The 3.5×–2DV sequence resulted in a higher permeation flux and lower energy consumption but required higher volume of water for CVD and increased volumes of permeate, which could lead to greater environmental impacts. A comparative life cycle assessment is currently underway to determine the best UF-CVD sequence in a sustainable development perspective.