Multicolored electroluminescent (EL) devices has been realized utilizing poly((1-dodecyloxy-4-methyl-1,3-phenylene)(2,5"-terthienylene))( hereafter, mPTTh polymer) as an emitting layer and tris(8-hydroxyquinoline) aluminum (A1q3) as an electron transport layer. A single layer EL device of mPTTh polymer emits orange-colored light. EL intensity increases as the thickness of A1q3 layer increases up to 30 nm, but the emission color becomes diversified when the A1q3 layer thickness is greater than 30 nm since the relative peak intensity of green EL from Alq3 layer grows. EL color is changed from orange to geenish orange depending on the thickness of A1q3 layer. EL efficiency of the double layer device was greatly enhanced by 3000 times in compared to that of single layer device. Alq3 layer in device acts as an hole blocking electron transporting layer and an emitting layer as a function ofthe thickness ofAlq3 layer.