To investigate the physical properties of sea tangle (Laminaria japonica) alginates, extracted by the Mexican process, the effects of extracting time and drying methods on intrinsic viscosities, MWs and DPs of alginates were examined. The MWs of alginates before and after dialysis decreased with increase of extracting time. The MW s before dialysis were lower than those after dialysis. The ash contents before dialysis decreased with increase of extracting time. After dialysis the ash contents of the alginates showed 10.4-10.9% of those, which were little affected by extracting time. In the ash composition after dialysis, the sodium content was 4.4 g/100 g, $90\%$ of total ash content. The ash contents, the intrinsic viscosities, the average molecular weight and the DPs of the alginates dried by AD before dialysis were higher than those by VF. The ash and uronic acid contents of alginates after dialysis showed $10.6-10.9\%;andl88.1-88.9\%$, respectively. But the intrinsic viscosities, the MWs and DPs of the alginates after dialysis gradually decreased by following dry methods. The decreased order was ADAD, ADVF, VFAD, VFVF. The coefficient of determination between MWs and DPs in the alginates having more than 300 kDa was 0.999.