Objective: To determine the knowledge on antibiotics use for acute upper respiratory tract infections (URIs) among the patients with this infection and to compare the knowledge among the patients with different demographic and social factors. Methods: Cross-sectional descriptive study was conducted by collecting data from 93 outpatients diagnosed as having URIs by physicians at the Queen Savang Vadhana Memorial Hospital, Chonburi during October 2012 to January 2013 by using a self-administered questionnaire. Results: Average score of knowledge on antibiotics among URIs patients was 2.5±1.9 out of 8.0. The majority had the score at 0-3 (77.4%). Most patients misunderstood that antibiotics were safe and no one had died from antibiotics use (91.4%), antibiotics reduced the symptoms of fever, runny nose, cough and sore throat (90.3%) and antibiotics were able to kill all pathogens (77.4%). Moreover, patients reading the campaign poster on rational use of antibiotics showed a significantly higher level of knowledge on antibiotics than those who did not read (p=0.022). Conclusion: Patients with URIs have inadequate knowledge on antibiotics use in this disease. The results of this study could be used as an input for planning patient education in the hospital on rational use of antibiotics.