The present invention relates generally to a method of synthesis of carboxymethyl iota carrageenan by substitute of new functional group onto iota carrageenan structure to increase its functionality. There is known method comprises of the steps of synthesis carboxymethyl iota carrageenan where soaking iota carrageenan in isopropanol and become a solution mixture, adding a strong base with the concentration range of 4-9 M into the solution mixturestirring the solution mixture, adding monohaloacetic acid solution into the solution mixture and become a carboxymethyl iota carrageenan solution, stirring the carboxymethyl iota carrageeenan solution, adding alcohol into the carboxymethyl iota carrageenan solution, filtering the carboxymethyl iota carrageenan solution to obtain a unpurified carboxymethyl iota carrageenan powder, and washing the unpurified carboxymethyl iota carrageenan powder with alcohol to obtain purified carboxymethyl iota carrageenan.