Japan have been using gonad index (KG) based maturity criterion for female chub mackerel of the Pacific stock with KG=3 as a sign of maturity. The present paper aimed to review the maturity criterion by estimating maturity probability curves based on KG and GSI using chub mackerel collected in 2013-2023, determining the maturity probability at KG=3, and comparing the annual changes in the threshold values for maturity based on KG and GSI. The review has found that KG=3 is a good indicator to extract only matured fish, however, its strict criterion labeled many individuals in early stages of yolk accumulation as immature. The 50% maturity KG showed a lower trend during 2019-2022 than during 2014-2018, whereas the 50% maturity GSI exhibited a relatively stable trend, hence GSI is considered a more appropriate maturity criterion. The 50% maturity GSI ranged from 1.6-1.8 in 2014-2023 and was 1.6 in the 2013-2023 integrated. This paper suggests that, in order to improve maturity-at-age (MAA) data for future stock assessment, it is more appropriate to use 50% maturity, notably GSI of 1.6 as the maturity criterion for stock assessment purpose, while noting KG=3 accurately designates maturation.