Abstract <p>To infer the effects of the sex ratio of the anadromous form on its dispersal pattern, we investigated the dispersal patterns of anadromous masu salmon in Toyama Prefecture. Toyama Prefecture is among the most southerly areas where the anadromous form is commonly found and thus its sex ratio is most biased toward females. In this study, to assess differences in dispersal patterns of anadromous masu salmon, we evaluated dispersal patterns using genetic assignment tests and compared dispersal patterns between sexes (male <i>vs.</i> female) and between two regions (Toyama <i>vs.</i> mid-western Hokkaido). Between 2019 and 2021, 366 anadromous masu salmon (141 males and 225 females) were collected from three rivers in the Toyama Prefecture and a genetic differentiation and genetic assignment tests were undertaken. The results showed that there was no dispersal bias between anadromous males and females in Toyama Prefecture, despite the small number of males in the anadromous fish. In addition, the dispersal rate at among-river scale in Toyama Prefecture (4.4% of all individuals) was slightly higher than that reported in the mid-western Hokkaido (2.9%), indicating that the dispersal tendency of anadromous masu salmon inhabiting Toyama is slightly higher than that in the northern region. This study suggests that the among-river dispersal of anadromous masu salmon may differ depending on region and that the influence of latitudinal variation of sex ratio on dispersal pattern may be expected.</p>