An attempt has been made in the present investigation to study variation of workability of fly ash based geopolymer concrete with the variation of lignin based plasticizer and poly-carboxylic ether based superplasticizer. It has been observed that there exists a critical value of molar strength of sodium hydroxide beyond which superplasticizer and plasticizer have adverse effect on workability of fly ash based geopolymer concrete. Below the critical molar strength of sodium hydroxide, there is an increase in slump. Lignin based first generation plasticizer shows better performance in terms of workability over third generation superplasticizer below the critical value of molar strength. It was also observed that there is a good correlation between the rheological parameters and slump for fly ash based geopolymer concrete incorporating plasticizer and superplasticizer.