The defect properties of semiconductors, especially those at grain boundaries (GBs) in polycrystalline semiconductor films, significantly influence their optoelectronic properties and consequently the performance of corresponding optoelectronic devices. However, despite extensive studies on GB defect properties in three-dimensional (3D) and two-dimensional (2D) semiconductors, research on GB defects in one-dimensional (1D) semiconductors remains unclear. Here, we report the intrinsic benign GB defect properties in 1D semiconductors, arising from their 1D crystal structure where no dangling bonds are present at GBs. Using the typical 1D optoelectronic material selenium (Se) as an example, we find that no defect states are introduced along the interchain direction of crystal planes through a combination of density of states and band structure calculations. We finally position the Kelvin probe force microscope probe on the cross-section of vertically oriented Se films to directly characterize the GB properties of polycrystalline Se films. We observe no significant changes in potential at the GBs, with the average plane potential difference being as low as approximately 10 mV, thus experimentally confirming the benign nature of GB defects in 1D materials. The combined theoretical and experimental results demonstrate the great potential of 1D semiconductors for optoelectronic applications.