Some colloidal suspensions contain two types of particles-small and large particles-to improve the lubricating ability, light absorptivity, and so forth. Structural and chemical analyses of such colloidal suspensions are often performed to understand their properties. In a structural analysis study, the observation of the number density distribution of small particles around a large particle (g(LS)) is difficult because these particles are randomly moving within the colloidal suspension by Brownian motion. We obtain g(LS) using the data from a line optical tweezer (LOT) that can measure the potential of mean force between two large colloidal particles (Phi(LL)). We propose a theory that transforms Phi(LL) into g(LS). The transform theory is explained in detail and tested. We demonstrate for the first time that LOT can be used for the structural analysis of a colloidal suspension. LOT combined with the transform theory will facilitate structural analyses of the colloidal suspensions, which is important for both understanding colloidal properties and developing colloidal products.