Non-durable flame retardant finish, borax/boric acid mixed solution, was applied to cotton fabric with pad-dry method. The LOI(limited oxygen index) was measured as the measare of the flame retardant effect. The TGA was investigated to know the thermal behavior of the samples. In addition, the solubility of the solutions was investigated. The results were as follows: 1) There was a synergism of flame retardant effect in the borax/boric acid mixed solution treatment and the maximum synergism was shown around the ratio of 7 : 3 2) After the borax/boric acid solution treatment, the degradation temperature was lowered and degraded at the larger temp range with slower rate. The residual char length also increased. 3) The solubility of borax/boric acid become higher when the ratio of borax/boric acid became similar. Compositions from 80/20 to 40/60 borax/boric acid mixtures were solubilized well in room temperatuare or warmwater therefor there was no problem for home use.