The influence of pH (2-9) and ionic strength (0-0.14 M NaC1) on the sol-gel transition of β-lactoglobulin was investigated in order to determine the critical gel concentration (Co). The concentration necessary to form a gel near the isoelectric pH remains approximately constant (~ 1% w/v) independently of the ionic strength. At other pH values, the higher the ionic strength is, the lower the protein concentration must be to form a gel. A theoretical model to relate the effect of the intensity and the range of electrostatic interactions on the critical concentration (Co) is proposed and fits reasonably with the experimental results.