This work describes an outbreak of strangles due to Streptococcus equi subsp. equi in 1 to 2 years old Thoroughbred horses. A total of 7 samples were collected from 5 horses in two different horse farms during 2003. Six ${eta}$-hemolytic colonies selected from each sample were identified by biochemical tests using API STREPTO followed by PCR amplification which is able to recognize unique region of SeM gene of S. equi subsp. equi. All colonies selected from the ruptured lymphadenitis of 2 horses in farm A were identified as S. dysgalactiae subsp. equisimillis. It seems to be secondary infection because the sampling sites have been already opened and the horses have been treated with antibiotics for a week. All colonies from 2 submandibular lymphadenitis samples in Farm B were S. equi subsp. equi while the isolates from 3 nasal discharges in this farm were mixed with S. equi subsp. zooepidemicus.