The Los Angeles Police Department said fire Capt. Matthew Phillipsen, 52, was caught during a sting operation in Highland Park, which is not far from the fire station where he's assigned.
Phillipsen allegedly tried to buy seven balloons of simulated heroin from the undercover officers around noon on Wednesday near Avenue 61 and Figueroa Street.
He was booked on suspicion of intent to possess heroin.
Los Angeles fire officials did not comment on the specifics of the arrest.
They released a statement, saying, "The matter is currently under investigation by the LAPD. The Los Angeles Fire Department's professional standards division has been notified and will be conducting an investigation concurrent with any criminal investigation."
Phillipsen was released after posting $10,000 bail. He is scheduled to appear in court Nov. 18.