Hynobius dunni is a species of salamander native to Oita, Japan. It is declining in numbers and was first listed “vulnerable” by the (IUCN) Red List of Threatened Species in 2004, with most recent reaffirmation being made in 2021. Much of Hynobius dunni’s behaviour remains unrecorded, including the full scope of its reproductive behaviour and their developmental stages. In hopes of future research and conservation efforts, both of the above were observed and recorded. Developmental stages were observed in lab settings. Data from the past were used alongside collected eggs. The eggs were kept in the incubator set to 7°C and 3 batches of different stages were observed at the same time. Each stage was illustrated and divided to its developmental stage numbers from 1 ~ 68, respective to the ones of Hynobius nigrescens (Iwasawa, Yamashita, 1991). Each stage was later compared to Hynobius nigrescens and similarities as well as few differences were observed, especially in later stages of development the differences stood out. As for their reproductive behaviour, gonadotropin was injected to both mature females and males, and were later put in the same tank. Their behaviours, from courtships to egg-laying, were recorded in captivity. The video was analysed and noticeable behaviours were divided into 3 main time frames: Post egg-laying, during egg-laying, and past egg-laying. Noticeable behaviours include: male and female clinging on to a twig; aggressive behaviours and attacks seen among dominant male; tail twitching etc. Midwife behaviour was also observed among Hynobius dunni males (Usuda, 1993). The correlation between twig clinging behaviour, courtship behaviour, and the result of the mate selection was analysed.