The viscoelastic property and scaling behavior of acid (glucono-delta-lactone)-induced soy protein isolate (SPI) gels were investigated at various ionic strengths (0-800 mM) and five protein concentrations ranging between 4% and 8% (w/w). The infinite storage modulus (G '(infinity)) and the gelation start time (t(g))which indicate the progress of gelation process exhibited strong ionic strength dependence. The storage modulus and critical strain were found to exhibit a power-law relationship with protein concentration. Rheological analysis and confocal laser scanning microscopy (CLSM) analysis were applied to estimate the fractal dimensions (D-f) of the gels and the values were found to vary between 2.319 and 2.729. The comparison of the rheological methods and the CLSM image analysis method showed that the Shih, Shih, Kim, Liu, and Aksay (1990) model was better suited in estimating the D-f value of acid-induced SPI gel system. (C) 2012 Elsevier Ltd. All rights reserved.