We aimed to examine mental health status and related factors among Vietnamese immigrants in Japan during the coronavirus disease 2019 (COVID-19) pandemic using data from an online cross-sectional survey administered from September 21 to October 21, 2021. Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder 7-item (GAD-7) scores were considered the main outcome measures. Multivariable logistic regression was used to identify factors related to symptoms of depression and anxiety, and the chosen variables were entered simultaneously in the survey. Among 621 participants (age: 26.0±4.8 years; male: 347 [55.9%]) who completed the questionnaire, 73.7% reported a decrease in income when compared with the period before the COVID-19 pandemic, and 60.4% reported being recently affected by poor socioeconomic status. Moderate-to-severe symptoms of depression (PHQ-9 score ≥10 points) and mild-to-severe symptoms of anxiety (GAD-7 ≥5 points) were observed in 247 (39.8%) and 285 (45.9%) individuals, respectively. Factors related to depressive symptoms were being single (odds ratio [OR]=1.76, p=0.042), medical or psychiatric co-morbidity (OR=2.15, p<0.001), and low socioeconomic status (OR=2.06, p<0.001). Factors related to anxiety symptoms were being single (OR=1.72, p=0.044), medical or psychiatric co-morbidity (OR=2.52, p<0.001), low socioeconomic status (OR=2.72, p<0.001), and absence of a partner with whom to discuss one′s health (OR=1.66, p=0.013). The current findings demonstrate that, when compared with Japanese citizens, Vietnamese immigrants experienced a decrease in income, worsening working conditions, and poor mental health status during the COVID-19 pandemic. These findings highlight the potential contribution of low socioeconomic status and social isolation to poor mental health status.