Composition-tunable semiconductor alloy nanowires are emerging as an important class of materials for the realization of high-performance laterally-arranged multiple bandgap (LAMB) solar cells. Here we report the first growth of GaZnSeAs quaternary alloy nanowires with composed elements between two different groups using a temperature/space-selective CVD route. Under laser excitation, these special quaternary alloy nanowires exhibit composition-related characteristic emissions, with peak wavelengths gradually tunable from 470 nm (2.64 eV) to 832 nm (1.49 eV), covering almost the entire visible spectrum. Surface photovoltage measurements further reveal that these alloy nanowires have tunable bandgaps along the length of the substrate, making them promising candidates for developing high-efficiency LAMB solar cells. These quaternary alloy nanowires represent a new advancement in material synthesis and would have potential applications in a variety of function-tunable and broadband-response optoelectronic devices.