The 32-year-old joined Al-Hilal from Paris St Germain for a reported 90 million euros ($A151 million) in 2023 but managed only seven appearances for them after suffering a serious knee injury.
"Playing football that's what I love the most. My family and friends already know my decision, I'll sign the contract with Santos Futebol Clube," Neymar said on a video posted on Instagram on Thursday.
"To be born, live and die for Santos is an honour only a few have ... I'm sure only Santos can provide the love I need to prepare for the coming challenges of the next years," he added of the club where the great Pele also made his legend.
Neymar began his career with Santos in 2009 aged 17, racking up 136 goals and 64 assists in 225 matches to help the club secure their first Copa Libertadores title in nearly 50 years in 2011.
He then joined Barcelona in 2013, winning two LaLiga titles, three Copa del Rey trophies and the 2015 Champions League.
Neymar has 128 caps and a record 79 goals for his country, surpassing Pele's tally of 77.
He was also part of Brazil's gold medal-winning squad at the 2016 Rio Olympic Games and helped them finish runners-up to Argentina in the 2021 Copa America.
He moved to PSG from Barca in 2017 for a world-record fee of 222 million euros ($A371 million) and won five French league titles with the capital club.
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