Urushi (Japanese lacquer) collected from lacquer trees (Toxicodendron vernicifluum) has been widely used as surface coating for centuries. Urushi is hardened by enzymatic polymerization with laccase which is included in raw urushi sap.In this reaction,temperature and humidity are essential factors. Generally, urushi hardens under 20-30 ℃ and 70-80 %rh. So, it is difficult to keep the condition in the case of outdoor coating in winter. In the present study, potassium tetrachlorocupurate (II) dehydrate (K2［CuCl4］･2H2O) was examined as an initiator to polymerize deactivated urushi.Urushi films with a catalyst (Cu-film) were prepared under 10-20 ℃ and 35-75 %rh conditions. Their surface appearances and chemical structures were examined by using a color meter, SEM, FT-IR and Py-GC/MS. In addition, a simplified copper elution test and a UV-C durability test were carried out. It was found that urushi film to which 0.5 wt% Cu catalyst was added (Cu0.5-film)was cured on similar curing time as that of ordinary raw urushi film (Std.-film) which was catalyzed by laccase under 20℃ and 75%rh condition (20℃,75%).Moreover,even under a low temperature and humidity environment, the catalyst-added urushi samples were properly cured:Cu0.8-film under 15 ℃,55 %;Cu1.0-film under 10℃,55% and 20℃,35%. Based on the FT-IR and Py-GC/MS analyses results, polymerization products of urushiol in Cu-films were approximately equivalent to those in Std.-film. To be more specific, it was suggested that crosslinking reaction of urushiol side chains had beenaccelerated.According to UV-C durability test,polyurushiol segments tend to remain more on Cu-film than on Std.-film. However, since excess catalyst provided increase of elution of Cu-ion in water, the amount of addition should be limited to the minimum.