Ge Minqiang and Liu Caikui, two other Rio executives, also admitted receiving bribes on the first day of the three-day trial.
The bribery charge could draw jail terms of up to 20 years, according to Zhang Peihong, a lawyer for one of the accused Chinese nationals, Wang Yong.
Hu, the former head of Rio Tinto’s iron ore operations in China, and his colleagues were arrested on suspicion of illegally obtaining commercial secrets and bribery at the height of fraught negotiations over 2009 iron ore prices.
It is understood Chinese steel mills paid the bribes to the Rio employees in order to win favourable iron ore deals.
The revelations are embarrassing for Rio Tinto and will add an element of wariness to already contentious iron ore negotiations with China.
Last year China’s crude steel output accounted for almost half the world’s total. Steel output and iron ore imports both soared to record highs in 2009.
The four men will have a chance to defend themselves today against charges that the bribes were illicit.
Their lawyers pointed out that admitting to accepting bribes did not necessarily mean that the defendants would plead guilty to charges.
The trial is a chance for China to reassure foreign investors that it is a safe place to invest and that its courts are transparent.