In X-ray fluorescence analysis, the fundamental parameter method (FP method) is often used for conducing quantitative analysis. If organic matter such as food, plant matter or resin is the principal component, the principal compounds are assumed to be CH2O and CH2, etc., and quantitative analysis is conducted regarding these components as balance components without conducting measurement. But when a resin sample is of indeterminate form or the quantity of food or plant matter is small, even if the presence or absence of elements can be determined, obtaining stable quantitative values can sometimes be problematic due to fluctuation of the X-ray fluorescence intensity. Therefore, taking into account these shape-related effects, a new feature of the background FP (BG-FP) method effectively provides stable quantitative values in analysis of such samples. Here we introduce an example of quantitative analysis of a small amount of hijiki (a type of seaweed) using the BG-FP method.