OBJECTIVE This study aimed to investigate the prevalence of and factors associated with depression in residents in training at the Faculty of Medicine, Chiang Mai University. METHODS This cross-sectional study was conducted with Faculty of Medicine residents in training from March to July 2020. We used the nine-item Patient Health Questionnaire (PHQ-9) to determine the level of depression. Binary logistic regression was used to evaluate associated factors: loneliness, burnout, sleep quality, emotional quotients (EQ), and perceived social support (PSS). RESULTS About one-fifth of the residents in training exhibited depression (47 of 201), and 6.97% had indications of suicidality. Factors showing a positive correlation with depression included loneliness (aOR: 1.27; 95% CI: 1.15-1.40); burnout scales of depersonalization (aOR: 1.18; 95% CI: 1.10-1.25), and reduced personal accomplishment (aOR: 1.10; 95% CI: 1.05-1.14). Factors showed a negative correlation with depression: perceived social support from significant others (aOR: 0.91; 95% CI: 0.85-0.98). Three subscales of EQ included motivation (aOR: 0.82; 95% CI: 0.68-0.99); life satisfaction (aOR: 0.83; 95% CI: 0.70-0.97); level of peace (aOR: 0.76; 95% CI: 0.66-0.87). CONCLUSIONS The prevalence of depression in residents was 23.40%. Loneliness, low social support, and burnout (depersonalization, reduced personal accomplishment) were all associated with depression. Three EQ factors (motivation, life satisfaction, and peace) appeared to have potential for reducing depression. KEYWORDS depression, resident training, loneliness, emotional intelligence, burnout