Broadband responsivity enhancement of single Se microtube (Se-MT) photodetectors in the UV-visible region is presented in this research. The pristine Se-MT photodetector demonstrates broadband photoresponse from 300 to 700 nm with peak responsivity of approximate to 19 mA W-1 at 610 nm and fast speed (rise time 0.32 ms and fall time 23.02 ms). To further enhance the responsivity of the single Se-MT photodetector, Au and Pt nanoparticles (NPs) are sputtered on these devices. In contrast to only enhancement of responsivity in UV region by Pt NPs, broadband responsivity enhancement (approximate to 600% to approximate to 800%) of the Se-MT photodetector is realized from 300 to 700 nm by tuning the size and density of Au NPs. The broadband responsivity enhancement phenomena are interpreted by both the surface modification and surface plasmon coupling. The experimental results of this work provide an additional opportunity for fabricating high-performance UV-visible broadband photodetectors.