Japan is one of the most earthquake prone countries in the world. Japan is affected by vari-ous damaging phenomena, such as liquefaction during earthquakes. Urayasu City had a big damage due to the great Eastern Japan Earthquake in 2011. In the survey results after earthquake, the particle size dis-tribution of the sand boiling contained a lot of silt. On the other hand, this research focuses on short fibers reinforcement as a new liquefaction restraint technique for the great earthquake. Short fiber mixed soil has the toughness effect so far, and it’s confirmed that liquefaction strength is increased. Therefore, this research is focused on the effect of fiber length on liquefaction properties of short fibers mixed soil con-taining fine-grain fraction. This study carried out undrained cyclic shear test using a short fiber mixed de-composed granite soil with different fine fraction contents. As a result, the liquefaction strength of short fiber mixed decomposed granite soil was found to be strongly affected by changes in the skeleton void ra-tio due to the fine-grain fraction contents. Also, this study revealed that the liquefaction suppression effect is difference by the fine grain fraction contents of short fiber mixed soil and there is an optimum content of short fiber length for liquefaction strength. This paper reports the effect of fiber length as a liquefaction suppression of short fibers mixed soil containing fine-grain fraction.