Experimental studies were done to know effect of insensible water loss of Hwangkitang(HKT) in mice. After administration of extract of HKT to the mice, changes of body temperature, body weight, serum Sodium and chloride ion was measured. And sametime, serum antibody to SRBC, delayed hypersensitivity and phagocytic activity of polymorphonuclear leukocytes(PMN) was measured to know immunologic effect. The results obtained as follows; 1. After exposure to $40^{circ}C$ environment, increment of body temperature in treated group was slower than control group during first 40 minute, and no difference after 40 minute. 2. After exposured to $40^{circ}C$ environment, decrement of body weight in treated group except administration group of 1.0g/kg extract of HKT was slower than control group during first 40 minute, and no difference after 40 minute. 3. After exposured to $40^{circ}C$ environment, decrement of body weight in administration group of 4.0g/kg extract of HKT to mice was slower than control group during first 20 minute(p<0.005). 4. After exposure to $40^{circ}C$ environment there was no stastical difference between treated group and control group in changes of serum sodium and chloride ion. 5. There was no statistical differences between treated group and control group in changes of serum antibody, delayed hypersensitivity and phagocytic activity of PMN.