The effects of 0–4.0% glucomannan and konjac noodles on the blood sugar level of cooked rice were elucidated by evaluating the sensory properties and by measuring the textural properties, thermal properties, blood sugar curve and glycemic index. The taste, flavor and appearance of the cooked rice containing the highest concentration of glucomannan were evaluated to be low and the texture was evaluated to be hard. The heating DSC curve showed, the endothermic enthalpy of the lower temperature peak to be increased and the endothermic peak of higher temperature to be increased in temperature with increasing glucomannan concentration. The blood sugar level was slowly increased and the maximum blood sugar level decreased by adding glucomannan. The maximum blood sugar level and glycemic index were significantly decreased by a mixture of only 28% konjac noodles.