"Raul knew that I would not accept a formal role in the party today," Castro said in an article on the Cubadebate.cu portal, referring to his brother Raul and his own absence from the party`s new Central Committee, elected on Monday.
Castro, 84, had served as first secretary in the Central Committee of the party -- which underpins the country`s Communist government -- since the party`s creation in 1965.
Fidel said he had handed over the functions of the party head to Raul when he ceded power to his brother because of his own declining health in 2006, though he retained the first secretary title.
"(Raul) has always been who I described as First Secretary and Commander in Chief," Fidel wrote in the article.
"He never failed to convey to me the ideas that were planned," he added.
The move came after the sixth Communist Party Congress approved a flurry of measures on Monday aimed at keeping Cuba`s centrally planned economy from collapse but without any broad embrace of market-oriented economic change.
The changes inject a modicum of the free market into the island`s economy ahead of a vote Tuesday expected to officially relieve 84-year-old Castro of his position as party head after more than four decades.
The 1,000 delegates gathered in Havana for the four-day party congress approved some 300 economic proposals and elected a new central committee leadership.
Reforms include the cutting of, eventually, a million state jobs, and decentralizing the agricultural sector.
Many of the measures have already been adopted over the past year, with the Congress now formally approving them.
Results of the voting on leadership term limits will be presented Tuesday, when Fidel, who ceded power to his brother when he fell ill in 2006, would be finally, officially replaced as party chief.
Raul, who turns 80 on June 3, likely would officially become the party`s new first secretary.
Raul Castro said on Saturday that he backed political term limits of 10 years at most for the top leadership spots, in a country he and his brother have led for more than five decades.
Focus will be also on the party`s number two position, which could possibly signal the direction of eventual transfer of power in the years to come.
Raul has rejected broader market-minded reforms like those adopted by China, saying they would be "in open contradiction to the essence of socialism... because they were calling for allowing the concentration of property."