We noticed the Urushi film, by which oriental lacquer wares are prepared. The effect of water on mechanical properties of oriental lacquer film was investigated in a tensile test and a stress relaxation test. These tests were conducted under the various degrees of humidity. Oriental lacquer film had a tendency to became brittle under dry condition and to toughen under wet conditions. On the other hand, the film becomes sticky and soft under high humidity or in water. The relaxation modulus for this film was determined under the various degrees of humidity. This behavior changed largely depending upon humidity. Master curves on the result of stress relaxation test were prepared by applying the rule of time-temperature superposition. The temperature dependence of shift factor on the various degrees of humidity could be represented by the Williams-Landel-Ferry equation by changing two parameters, C-1 and C-2.