The demersal lizard fish widely distribute from the sub-tropical area to the tropicalarea.They include four major species in the Southern Taiwan Strait,i.e.,Saurida undos-quamis,S.tumbil,S.elongata,and S.gracilis.Among them,the S.undosquamis occupies67.15% of the lizard catch in gross weight.The specimens used in this study were sampledmonthly from the landings of the baby trawlers that operated in the Southern Taiwan Straitfrom May 1992 to December 1993 at Kaohsiung Gusan Fish Market.The vertebra agecharacter was adopted to be ring-read.The age compositions in 1992 and 1993 were estimatedfrom the joint length frequency data and the observed age-length key tables using the iterativeage-length key algorithm(IALK).The results are as follows:There had 10 age groups from age 0 to age 9 in 1992 and 9 age groups from age0 to age 8 in 1993.The major catch group appeared at age 2 in 1992 and age 3 in 1993.The high R^(2)values indicate that the results might be credible,and that the IALK couldbe a reliable method.