Tokyo, Alibaba Co-founder Jack ma has stepped down from the board of Japanese conglomerate SoftBank Group after serving it for nearly 13 years, the company announced on Monday.

The heavily indebted SoftBank did not give any reason but Ma has slowly been moving away from daily roles towards philanthropic work.

Ma is close with SoftBank founder and CEO Masayoshi Son.

Son invested $20 million in Alibaba in 2000 — a bet that turned into $60 billion when Alibaba went public in 2014, according to CNN.

SoftBank has since sold some shares, but its 25.1 per cent stake in Alibaba was still worth more than $133 billion.

Ma is the only director out of SoftBank Group's current 11 directors who is leaving the position.

SoftBank also said it nominated three new board directors for election at the shareholders meeting: SoftBank Group chief financial officer Yoshimitsu Goto; Cadence Design Systems chief executive Lip-Bu Tan; and Waseda Business School professor Yuko Kawamoto.

Ma stepped down as Chairman of the multi-billion dollar e-commerce behemoth Alibaba in September last year.

Ma resigned as Alibaba's CEO on May 10, 2013.