The effect of carrageenan concentration on thermal phase transitions of the iota carrageenan gels was investigated by using fluorescence technique. During heating and cooling processes, scattered light, I(sc), and fluorescence intensity, I(p), were monitored against temperature to investigate phase transitions. Transition temperatures from the derivative of the transition paths were determined. Two regions were observed during the heating and cooling processes. At the first step of the heating, dimers were converted into double helix by undergoing dimer to double helix (d-h) transition. At the higher temperature region, double helix to coil (h-c) transition took place. During the cooling process, these transitions are arranged in the order of coil to double helix (c-h) and double helix to dimer (h-d). A hysteresis was observed between (h-d) and (d-h) transitions. The critical gel fraction exponents, beta, were found to be independent of the system by indicating that they all fall into the same universality class. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2652-2661, 2011