Introduction: In an epidemic, health-care providers (including medical residents) are in the risk of infection. Their proper compliance to the epidemic would lead to the successful management of the epidemic. The aim of this study was to assess the medical residents’ knowledge, attitude, and practice (KAP) about influenza (H1N1) and its vaccination in H1N1 provincial referral hospitals in Tabriz, Iran. Methods: Using cross-sectional descriptive design, this study was carried out from 25 January to 30 March 2015 (during the epidemic). All the medical residents in three H1N1 provincial referral hospitals (220 individuals) in Tabriz were included. A valid questionnaire was used for data collection. Results: Over 51% of the participants were male. The mean score of knowledge and attitude about H1N1 were 53.5 and 62.2, respectively. There was no significant difference (P > 0.05) between the residents who had uptake influenza vaccine and who refused in Knowledge level. Vaccination rate was calculated as 73%. “Fear of influenza infection” (34.6%) and “health facilities recommendation” (30.8%) were the main reasons of vaccination. Conclusions: Health authorities and medical universities must employ proper policies to improve the medical residents’ knowledge about H1N1. Furthermore, vaccination facilities must be provided in hospitals to increase the vaccination rate.