Kim Jong Nam, 39, made his comments during an interview in Beijing for Japanese TV network Asahi.
"I personally oppose the power transfer to the third generation," said Kim Jong Nam. "However, North Korea might have its own internal factors that forced it to pass power to a third generation. I believe that they had to follow the internal factors."
His remarks come after an extraordinary meeting last month of the secretive North Korean state's ruling communist party in which began the political elevation of his brother, Kim Jong Un, believed to be 27, to be the eventual ruler.
Kim Jong Nam's comments appear to fly in the face of their father's chosen successor, the younger brother, to take the government helm in Pyongyang.
But how much influence the elder son wields within North Korea is open to question. Some political analysts wrote him off as a serious political contender when he embarrassed his father in May 2001.
Japanese authorities detained him at Tokyo's Narita airport for attempting to enter the country illegally with a Dominican passport. Kim Jong Nam reportedly told officials he was going to visit Tokyo Disneyland.
But he arrived from Singapore with two women and a 4-year-old boy. The younger of the two women was said to be Jong Nam's secretary and Japanese interpreter. The child was his son but it wasn't clear whether the other female companion was his wife, Shin Jong Hi, or a relative who takes care of the child.
Also, it wasn't his first illegal visit to Japan, airport officials later confirmed, and he was summarily deported to Beijing where he spends most of his time, as well as in Macao.
Despite his being sidelined for North Korea's most senior political job, and his apparent swipe at dynastic rulers, he also said he nonetheless would support his younger sibling should he rise to the top.
"Kim Jong Un has become the heir apparent under the determination of his father," he said during the Asahi TV interview.
"I hope that my younger brother Jong Un would do his best so that North Koreans could live a comfortable life. I'm always ready to support my brother overseas whenever he requests."
His out-of-step attitude with his father also may be a result of maternal issues. Kim Jong Nam was born in 1971 to Song Hye Rim, considered to be Kim Jong Il's second wife, the intelligence Web site globalsecurity.org said.
But there are questions over whether his father married Song, meaning Kim Jong Nam may be illegitimate, and not eligible of being a dynastic ruler in North Korea. Song soon fell out with Kim Jong Il and moved to Moscow.
At the age of 10, Kim Jong Nam was sent to study at an international school in Geneva and so began his international wanderings that would take him further from the political center of North Korea.
During the Asahi TV interview, and in his typically ambiguous manner, Kim Jong Nam referred to North Korea as Bukhan, the name South Korea would use when referring to the North. North Koreans call it Joseon.