A new method for the investigation of the gelation behavior of soy proteins is proposed Soy protein isolate was used to prepare a soy protein solution and glucono-delta-lactone was used as a coagulant. L*, a* and b* values of the CIE 1976 (L*a*b*) system were continuously, monitored with a colorimeter. The stability of this system was confirmed with 13 replicates of control soy protein dispersion. Nine replicates of soy protein solution with coagulant under the same conditions were carried out to estimate the observation error. It may be possible to use L*, a* and b* values as a reliable measure of the change within the aggregation/gelation process due to the large change with a small variability given by L*, a* and b* values. Changes in structure during each step of the process were revealed by Scanning Electron Microscopy and were consistent with the results from the surface color measurements.