We studied gelation behavior of aqueous solution of agarose (1.0wt%) using light scattering and rheological measurement. Aqueous solution of agarose (1.0wt %) showed a stepwise structural evolution via a series of stages when it was cooling very slowly from the solutions. The stage includes: i) Homogeneous solution at above 62°C; ii) inhomogeneous transition stage at 61°C-51°C, where the mean scattering intensity steadily increased with temperature drop; iii) homogeneous intermediate state at 50°C-38°C, where scattering intensity stays constant; iv) second transition stage at 37°C-34°C, where scattering intensity rised steeply; and v) typical gel state at below 34°C. All states below 62°C showed hysteresis in that the return to solution required reheating to above 93°C. Because the loss modulus G'' was close to the storage modulus G' in the state iii), the phenomenon at this temperature range seems to be a weak gelation. Large fluctuations of scattering intensity in time and/or space observed in the stages ii) and v) indicate the presense of mobile or frozen-in inhomogeneities.