The study was conducted on antibiotics use and determinant of use on 101 broiler farms in Songkhla province, Thailand. Ninety-six farms used the broiler production system under contracting companies and 5 farms were independently operated. All of the farms used antibiotics for disease prevention. Twenty agents in 9 classes of antibiotics were used; the most commonly used ones were enrofloxacin, amoxicillin, doxycycline, colistine and roxithromycin. There were 33 patterns of antibiotics use, the most frequently used being the combination of amoxicillin-enrofloxacin (21.18%). Cluster analysis suggested that the variation in antibiotic usage is mostly under the influence of the companies. Regulation of antibiotics use thus should focus on the company level.