Cell walls of the marine Oomycete, Atkinsiella dubia were prepared and an analysis of the wall constituents was made. The walls contained approximately 80% polysaccharides and 14% proteins along with small quantities of lipid and ash. The carbohydrate fraction was composed primarily of glucan along with 1.8% glucosamine and a trace of galactosamine. An analysis of the amino acid composition of the protein fraction showed the presence of 18 identified amino acids including a surprisingly high (20% of total amino acids) hydroxyproline content. The polysaccharide fractions of the wall were mostly glucans with solubility properties similar to those reported for other Oomycetes. As anticipated, the glucans of mechanically isolated walls were virtually identical to those prepared from chemically isolated walls. The minor glucan component, cellulose, was found to occur in the form of poorly crystalline cellulose I As expected, electron microscopy of wall specimens showed microfibrillar and amorphous regions. It was stressed that Atkinsiella walls, like those of other Oomycetes, contain large quantities of β-1→3 and β-1→6 linked glucan along with a smaller amount of cellulose.