To extend utilization of alginate from the sea tangle, Laminaria japonicus, depolymerized alginates (HAG-10, average molecular weight 10,000; HAC-50, average molecular weight 50,000; HAG-100, average molecular weight 100,000) were obtained by hydrolysis of alginate by heating at $12^{circ}C$. The effects of each depolymerized alginate on excretion of cholesterol, glucose and namium in rats were investigated. The total excretion rate (${\%}$) of cholesterol and cadmium was the highest in rats administered with HAG-50, The rate was $45.81{\%} and 59.02{\%} with HAG-50$. It was high in the order of $45.78{\%} and 56.05{\%}$ in HAG-100, $41.28{\%}$ and $55.96{\%}$ in alginate, and $32.11{\%} and 44.92{\%} in HAC-10$, respectively. In the case of HAG-50, it significantly (p<0.01) prevented the serum glucose level of rats from rising within 30 min and 60 min after glucose loading or administration among all the samples, but it had no particular effects on the serum insulin level. In conclusion, it was suggested that HAG-50, in which the alginate had a decreased molecular weight, while still retaining its desirable functions as a dietary fiber, was effective in excretion of harmful substances, such as cadmium and cholesterol, and in lowering glucose activities in serum of rats.