<p>The cloud point of biodiesel refers to the temperature at which crystallization begins on cooling. However, solidified products are often formed during storage even at a higher temperature than the cloud point. Such solidified products are known to consist largely of monoglyceride due to its high melting point. In addition, monoglyceride has polymorphism such as α, β' and β-types (melting point: α < β' < β), causing complicated behavior of biodiesel at low temperature. In this study, therefore, the effect of monoglyceride polymorphism was studied on low-temperature fuel properties of biodiesel. As a result, it was found that the cloud point relates to the formation of α-type crystal, whereas the solidified products formed at a higher temperature than the cloud point are considered to be β'-type. It implies that the concept of the cloud point generally accepted is not appropriate as an index of low-temperature fuel property of biodiesel.</p>