The thermal stability and catalytic activity of endoglucanase(EngD)from thermophilic Thermotoga maritima were significantly improved by rational design on the basis of our previous Directed evolution.The activity of two mutants,K207G and E225H,increased to varying degrees comparing with original enzyme.The relative activity was improved 30.38%and 29.62%respectively.The enzymatic properties of the purified mutant proteins were determined.The results show that the optimum temperature of recombinated endoglucanase Cel12B-207 is 95℃,the optimum pH is 7.4.The left enzyme activity hold 70%compared to the unkept one after putting in 90℃ for 2 hours.The optimum temperature of recombinated endoglucanase Cel12B-225 is 75℃,the optimum pH is 6.6.The left enzyme activity hold 95%compared to the unkept one after putting in 75℃ for 8 hours.