A detailed study of gametes development and characterization of plasma sex steroid hormones during the maturation cycle was performed for the first time in the southern hake (Merluccius australis). Fish were caught in the inland waters of the Reloncaví Sound, Interior Sea of Chiloé, Chile. Samples of gonads and blood were collected for histology and sex steroid hormone (17 β-estradiol, 11-ketotestosterone and 17,20 β-dihydroxy-4-pregnen-3-one) analysis, respectively. Sex steroid hormone quantification was performed using enzyme-immunoassay (ELISA). Results showed that M. australis males and females have asynchronous development of testicles and ovaries, in all stages of maturation. Most spawning fish were found during the spring months. Regarding the sex steroid hormones, serological fluctuations of 17 β-estradiol and 11-ketotestosterone were found during gonadal maturation of M. australis. These hormones are the main hormones responsible for vitelogenesis and spermatogenesis processes, respectively. Conversely, 17,20 ß-dihydroxy-4-pregnen-3-one did not show any serological fluctuation in females and males. Further studies involving gonadotropins, 17,20 β,21-trihydroxy-4-pregnen-3-one and vitellogenin quantification are required in order to obtain a more complete description of the reproductive physiology of wild and farmed M. australis.