We investigated body shrinkage, def ined 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: SLoriginal = 0.96SLpreserved + 5.17 and BWoriginal = 1.16BWpreserved + 0.37. These equations will be useful for improving accuracy the estimation accuracy for various size-related biological parameters in juvenile chub mackerel juvenile.