<p>Recently, the number of households in developed countries that have both dogs and cats has increased. Surveys of pet owners in Western countries have generally found positive relationships between cohabiting dogs and cats, with age at cohabitation onset and cat-specific factors being the main determinants of amicability. However, no study has examined this relationship in Japan or any other Asian context. Exploring the dynamics of dog–cat relationships in diverse cultural settings is important for the welfare of both species. This study, therefore, used an online survey (<i>N</i> = 777) to assess Japanese pet owners’ perceptions of dog–cat relationships within the same household. Stepwise linear regression was used to model the predictors of perceived amicability. Similar to previous findings, most owners reported that their dogs and cats were comfortable with each other and had friendly relationships; a younger age of introduction strongly predicted greater amicability. Different from prior findings, however, both ‘dog factors’ (e.g. comfortableness around cats, showing toys) and ‘cat factors’ (e.g. comfortableness around dogs, absence of threatening behaviour) significantly influenced owners’ perceptions of amicability. By providing insights into dog–cat cohabitation in Japan, this study contributes to cross-cultural research and has practical implications for pet welfare and management.</p>