The objective of this study was to estimate genetic parameters of main length ratios associated with morphological traits in Paralichthys olivaceus. At 180, 240 and 360 days of age, body length (L1 ), head length (L2 ), body depth (L3 ), caudal peduncle depth (L4 ) and caudal-peduncle length (L5 ) were observed in 4757-5224 individuals from 52 full-sib families. Based on these observed traits, the main length-ratio traits including L3 :L1 , L2 :L1 , L5 :L1 and L4 :L3 were constructed. Three single-trait animal models were used to examine the phenotypic variation of length-ratio traits and were compared using the likelihood ratio test. As a result, the optimal model for all the analysed traits was determined as the model with the fixed, additive genetic and full-sib family effects. Using the optimal model, animal model analysis for single trait showed that heritabilities were estimated to be low, ranging from 0·122 to 0·276. The estimates for all length-ratio traits decreased while the days of age increased except for L3 :L1 . Multivariate animal model analysis indicated that within and among days of age, genetic correlations between length-ratio traits were different in the direction and magnitude. Genetic parameter estimation of main length ratios would be helpful for genetic improvement of body shape in P. olivaceus.