We investigated body shrinkage, defined as change in standard length and body weight of juvenile chub mackerel Scomber japonicus after preservation in 70% ethyl alcohol for 1, 8, or 12 days. Standard length (SL) was decreased by 3.6% and body weight (BW) was reduced by 27.5% after 8 day of preservation. There were no significant decreases in SL and BW after 8 or 12 days preservation. Linear regression equations for estimation of original body size from the size after preservation in 70% ethyl alcohol for 12 days were expressed as: $SL_{original}=0.96SL_{preserved}+5.17$ and $BW_{original}=1.16BW_{preserved}+0.37$. These equations will be useful for improving accuracy the estimation accuracy for various size-related biological parameters in juvenile chub mackerel juvenile.