The relationships between guluronate content (G%) in alginates determined by 1H-NMR spectroscopy and their weight average mol. weight (WAMW) were examined to evaluate the reliability of the 1H-NMR method.The partially hydrolyzed alginates with WAMW of 15k, 30k, 45k, 60k and 100k were prepared from alginates with WAMW of 150∼200k by autoclaving.The G% in the partially hydrolyzed alginates determined by 1H-NMR spectroscopy were independent on their WAMW, when the G% was less than 70%.The 1H-NMR spectroscopic method using partially hydrolyzed alginates prepared by hydrolysis in an autoclave might be a convenient and reliable for the determination of G% in alginates.