The effects of membrane pore size and operating pressure on filtration flux, membrane fouling and solute rejections of soymilk during ultrafiltration were studied. Soymilk was concentrated from an initial level of 6.5% solid content to 20% solid content using ultrafiltration membranes. Hollow fibre cross-flow type cartridges having molecular weight cut-off (MWCO) as 1, 10 and 30 kDa were used in the experiments. Filtration data were satisfactorily fitted to De La Garza and Boulton's exponential model to find the exponential fouling coefficient (k) and the membrane resistance (Rm). The permeate fluxes obtained in 10 and 30-kDa MWCO membranes were found to be approximately four times higher than that of 1-kDa MWCO membrane, at transmembrane pressure between 100 and 240 kPa. The average flux obtained was 0.7, 3.15 and 2.7 L m−2-h for 1, 10 and 30-kDa MWCO membranes, respectively. The Rm value of membranes was found to decrease as the MWCO of membranes increased and transmembrane pressure decreased. The total solid content of permeates obtained by these membranes was between 0.45% and 1.4%. Membrane-concentrated soymilk was found to have lighter colour and almost half the value of viscosity compared with evaporated milk.