The $230 million upgrade will increase the shiploading capacity, together with rail stock handling volumes, at Dampier port's Parker Point facility by the end of first quarter (Q1) 2012.
The investment will be in addition to the $91 million commited in early 2010 to increase the Pilbara region's iron ore capacity from 220 to 225 Mt/a by the end of Q1 2011.
"Rio Tinto's Parker Point facility at Dampier port is our single largest and busiest port operation," said Sam Walsh, Rio Tinto chief executive of iron ore and Australia.
"We will actively manage this incremental expansion to maintain production and expansion schedules, consistent with our record of orderly and timely delivery of additional iron ore supply.
"These additional tonnes will come from our existing west Pilbara operations at Nammuldi and Brockman 2 (Rio Tinto share 100%), and without any additional investment in the mines.
"This incremental capacity will add substantial value and will position our integrated Pilbara operations well as we finalise plans on how best to move to a 330 Mt/a capacity and beyond."
Meanwhile, the company is undertaking feasibility studies in plans to increase the port's capacity to 280 Mt/a by the end of H2 2013.
Rio Tinto hopes to increase the iron ore capacity at the Pilbara region to 330 Mt/a by the end of second half (H2) of 2015.
Rio Tinto is a leading international mining group headquartered in the UK, combining Rio Tinto plc, a London and NYSE listed company, and Rio Tinto Limited, which is listed on the Australian Securities Exchange.