The Florida resident allegedly blew a 0.19, more than twice the legal limit, according to TMZ, which first reported the L.A. court news.
That's Cassidy's third DUI arrest and the second in a little more than six months.
He was arrested in New York in August and charged with felony DUI after reportedly blowing 0.10 on a blood-alcohol test. He'd recently completed rehab, his manager-rep told "Entertainment Tonight" in January, but had relapsed after the pressure of a deposition and planned to return to rehab.
In February 2011, Cassidy cut a deal that saw him pleading no contest to misdemeanor DUI in Florida in exchange for a year's probation and six months with a suspended driver's license.
He'd been arrested there the prior November after weaving on a parkway; he blew a 0.14 on a blood alcohol test, failed a field sobriety test and had an open bottle of bourbon in the car, police said at the time.
Speaking to "ET" from rehab on Wednesday, Cassidy said: ”This has been a very difficult time for me battling this deadly disease, like millions of others in our country. I will remain in treatment for as long as necessary and I am getting the best care I can possibly get anywhere. I am working as hard as any human being to live a sober life. "
He expressed gratitude for the support he'd received from friends and fans.
Cassidy's New York case has been put on hold because of the arrest in L.A., according to channel WRGB in Albany, N.Y., which said the prosecution and defense planned to meet again in March to discuss the situation.