The mistrial was declared at midnight Thursday, officials say.
The D.A.'s office says it was a hung jury and there has been no formal decision on whether there will be a retrial.
Authorities say 60-year-old Edward O'Brien III was the designated caretaker for his elderly father, 92-year-old Edward O'Brien, Jr.
On September 8, 2013, police responded to the younger O'Brien's home on the 900 block of Hollyview Lane in West Whiteland Township and found his father dead, covered with bedsores and feces.
The D.A. says O'Brien III had removed his father from a rehabilitation facility over two years before his father was discovered. He then allegedly allowed his father to die from neglect.
O'Brien III is also accused of stealing $30,000 from his father.
Last April, Joseph P. Green, the attorney representing Mr. O'Brien, released the following statement:
In 2011, Ed's 91-year-old father asked Ed to spare him death by nursing home, and Ed agreed. He moved his Dad into his home in Exton, and devoted the next two and a half years to caring for his father.
The elder O'Brien was a veteran of the United States Army, where he served from 1942-45. He later worked for the United States Postal Service.
His son, Edward, was his only child.
District Attorney Tom Hogan responded at the time by saying, "This was not a matter of someone who was diligently looking around for options. This was someone who put their father in a back bedroom to rot."
Hogan added, "As a veteran, the victim could have received medical care from the Southeastern Pennsylvania Veteran's Center. As a resident of Chester County, he could have received care at the Chester County Pocopson Home. Instead, as a result of the neglect of his own son, the victim died in filthy conditions and without any medical care. This was a death without dignity."
Edward O'Brien III was charged with Third Degree Murder, Theft, and related offenses.