A spectrophotometer was used to measure the turbidity of a carrageenan gel as a function of temperature. The optical transmission of the gels was found to decrease as the gels undergo the sol-gel phase transition. The differential of transmission (I) with respect to temperature (T), dI/dT, exhibits peaks for both the cooling and the heating runs with the peak. positions corresponding to temperatures of gelation and melting, respectively. The full-width at half-height of the dI/dT peak obtained from the heating curve is about 2.5 times broader than that from the cooling curve. This indicates that the melting of gels may involve multiple relaxation mechanisms. The area of the hysteresis loop covered by the cooling and the heating curves increases with a decrease in the scanning rate. The thermal cycling has little impact on the sol-gel transition in the gels. The experiments show that turbidity is a powerful tool for studying the sol-gel transition in carrageenan gels.