A lamp body for a vehicle lighting unit includes a PC/PTT alloy material in which 80 to 50% by weight of a polycarbonate resin (hereinafter referred to as a PC) and 20 to 50% by weight of a polytrimethylene terephthalate resin (hereinafter referred to as a PTT) are contained as principal components and 5 to 10% by weight of a filler is added with respect to the total weight of the PC and the PTT. The lamp body constituted by the PC/PTT alloy material can be thermally welded to a lens formed of the PC, and has a heat resistance, a chemical resistance and a bending rigidity which are almost identical to those of a lamp body formed of a polypropylene. Therefore, the lens and the lamp body can be bonded and integrated by a thermal welding method.