PURPOSE: To produce a protoplast of laver effectively applicable to cell fusion, by treating lavor leaf bodies with an enzymic solution obtained by cultivating a microorganism belonging to the genus Pseudomonas.

CONSTITUTION: A microorganism, e.g. Pseudomonas sp. PT-5(FERM-P No.330), belonging to the genus Pseudomonas, and having the ability to hydrolyze slightly digestible polysaccharides is cultivated in a culture medium containing a plant body containing polysaccharides having β-1,3-xyloside bonds and β-1,4-mannoside bonds as a structural polysaccharide component other than laver leaf bodies or the above-mentioned polysaccharides derived from the above-mentioned plant body as an inducer, and an enzymic solution containing at least xylan hydrolase and mannan hydrolase and further porphyran hydrolase is obtained from the culture fluid and used to treat the laver leaf bodies which are if necessary pretreated with protease.