Abstract: In this study, the age and growth of Dosidicus gigas were investigated by analyzing the microstructure of upper beak rostrum sagittal section (RSS), based on 148 specimens collected from the open sea of Chile. The results show that its RSS was composed of hood and crest, where periodic growth bands including one light and one dark increment were distinct. The increments of hood and crest met together at the region of internal rostral axis, showing a pattern of ‘<’. The stress marks and aberrant structures might relate to special ontogenetic events or external accident. The back−calculated hatching date was deduced from March to November, mainly from June to July in 2009. The relationship between mantle length (ML) and age can be described as power function. The average IGR (Instantaneous growth rate) and AGR (Absolute daily growth rate) of ML of female D. gigas were 0.14 %˙d⁻¹ and 0.60 mm˙d⁻¹, respectively, and the average IGR and AGR of ML of males were 0.11 %˙d⁻¹ and 0.47 mm˙d⁻¹, respectively. The results can provide not only a new method for age and growth study of Ommastrephidae but also important references for Chinese scientists to perform relevant researches.