Andrew Forrest has purchased 1.75 million shares in iron ore giant Fortescue Metals Group for about $7 million.
A change of director's interest notice showed a purchase of the shares by Mr Forrest for an average price of $3.97 a share.
Mr Forrest now holds 1.033 billion shares in the company.
The trade follows subsantial falls in the FMG share price in response to a big drop in the iron ore price, which currently sits around $US90 per tonne.
Earlier in the week, Sundance Resources' non-executive director Andrew Marshall picked up 500,000 shares in Sundance at a cost of about $43,900.
FMG's share price today rose by 4.98 per cent to $4.22 at 3.25pm WST.