Fine roots are one of major components of below-ground carbon flux. Therefore, it is needed to better understand fine root dynamics to deepen our understanding of carbon dynamics in forest ecosystems. The minirhizotron technique is currently a popular method to analyze fine root dynamics. One of advantages of this technique is that growth, death and decomposition of individual fine roots can be observed non-destructively, which enables us to analyze phenology or life span of fine roots directly. On the other hand, the minirhiztoron technique needs conversion of data under some assumptions to estimate fine root growth rates per unit stand area or per unit soil volume, because data directly obtained by this method are two dimensional images on the surface of transparent tubes (minirhizotrons). I have been working on fine root dynamics in some forest stands in Japan (e.g. Cryptomeria japonica stand) using a minirhizotron technique. In this presentation, I will overview characteristics of the minirhizotron technique and talk about fine root phenology based on the results of our studies. In addition, possible approaches will be discussed for data conversion to estimate fine root growth rates from two-dimensional minirhizotron data.