AbstractTo understand a biological system, it is important to observe structures of biomolecules in the solution where the system is functionalized. Small-Angle X-ray Scattering coupled with Size Exclusion Chromatography (SEC-SAXS) is one of techniques to selectively observe the target molecules in the multi-component system. However, this technique is believed to be available only with a synchrotron-based SAXS instrument due to requirement of high beam intensity and, therefore, the limitation of the beam time was obstacle to satisfy demands from many bio-researchers. We newly developed Laboratory-based Size exclusion chromatography SAXS System (La-SSS) by utilizing a latest laboratory-based SAXS instrument and finely optimization of the balance between flow rate, cell volume, irradiation time and so on. La-SSS succeeded not only decoupling of target protein(s) from non-specific aggregates but also measurement of each concerned component in a multi-component system. In addition, an option: “stopping mode”, which is designed for improving statistics of SAXS profile, realized a high S/N data acquisition for the most interesting protein in a multi-component system. Furthermore, by utilizing a column having small bed volume, the small-scale SEC-SAXS study makes available. Through optimization of instrumental parameters and environments, La-SSS is highly applicable for experimental requirements from various biological samples. It is strongly expected that a La-SSS concept must be a normal option for laboratory-based SAXS in the near future.