The islands of the Caribbean have been affected by an influx of Sargassum natans on their beaches. Sodium Alginate may be extracted from the cell walls of Sargassum natans, and its derivatives have many useful applications in a number of areas including the chemical, cosmetic, medical fields and also as a bio-absorbent of heavy metal ions in wastewater treatment. In modelling this absorption, a knowledge of the molecular weight (Mw) of the algi-nate would aid in the understanding of the interaction between the monomers of the algi-nate and the heavy metal ions. In this work, the intrinsic viscosity [η] of fours alginates – three commercial (Sigma-Aldrich, Manugel LBA and Protanal LF) and one extracted from Sargassum natans obtained from the East Coast of Trinidad – was determined via single-point and multi-point dilute solution vis-cometry methods. A size OB Ubbelohde viscometer and a Cannon CT 600 Constant Tem-perature Bath was used here. Using these viscosities along with values of Mw obtained in-dependently via Gel Permeation Chromatography (GPC), the constants in the Mark-Houwink-Sakurada (M-H-S) Equation, for alginates of this molecular weight Mw size range were determined. Using the alginate extracted from the Sargassum natans, a concentration range of 0.10 to 0.05 dL g-1 was determined to be most suitable for carrying out multi-point analysis. The algi-nates used had values of Mw between 296 and 669 kDa and the [η] values were determined to be between 2.47 and 8.69 dL g-1. The constants in the M-H-S Equation were determined to be K = 1.44 X 10-4 dL g-1, and a = 1.70 for the multi-point method and for the single-point methods the average values were K = 1.69 X 10-4 dL g-1 and a = 1.67. The [η] vs Mw data fitted the M-H-S equation with a correlation of 0.97. The significance of this work is that once the M-H-S constants are known, the values of the Mw of the alginates may be determined via dilute solution viscometry rather than more de-tailed and expensive methods such as GPC.