Method of producing polysaccharide derivatives

A method of producing a polysaccharide derivative comprising a polysaccharide having a carboxyl group bound to an organic compound having a functional group capable of condensing with the carboxyl group,

• which comprises reacting the polysaccharide with the organic compound by the use of a condensing agent shown by the general formula (1):
• wherein R1 and R2 independently represent a substituent selected among alkyl groups of 1 to 4 carbon atoms and aryl groups of 6 to 8 carbon atoms;
• Z−represents a counter anion;
• and E+represents the following group:
• wherein R3, R4, and R5 independently represent an organic group having at least one carbon atom directly bound to the quaternary nitrogen atom and any two or all of R3, R4, and R5 may link together to form a cyclic structure,
• wherein the polysaccharide having a carboxyl group is a hyaluronic acid having a weight average molecular weight of 100,000 to 5,000,000, and
• wherein the rate of the introduced organic compound per disaccharide unit of the hyaluronic acid is not less than 5%.