The government is being pressured to do more to oppose whaling following the dramatic collision between a conservationists' boat, the Andy Gil, and a Japanese whaling ship in the Southern Ocean on Wednesday.
Ms Gillard said the government was taking action by collecting evidence about the killing of whales and putting diplomatic pressure on whaling countries.
The government has been accused of allowing Japan's importance as an export market to cause it to break a promise made before the 2007 election to take international legal action over the issue.
"Well, before you can go to court, you have got to collect the evidence and we have done that as a government," Ms Gillard told the Nine Network.
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"The first thing we did is we got the Oceanic Viking out during a whaling season to collect the evidence.
"And then knowing that we have the evidence we have been pushing through the International Whaling Commission, through our envoy on whaling and directly with the Japanese government for an end to the killing of whales for so-called scientific purposes.
"Now what we have said is our patience is not endless. If we are not going to get a result diplomatically, we have made it very clear that a course of action open to us is international legal action."
Ms Gillard said the government was pressing for a restructuring of the International Whaling Commission to put environmental issues at the forefront of what it did.
The comments come amid fears of escalating clashes between Japanese boats and protesters from the Sea Shepherd group, and Ms Gillard urged ship captains to protect all people involved.
On Friday, Japanese authorities criticised conservationists for abandoning the Andy Gil at sea and claimed it was leaking fuel. The Sea Shepherd group said the vessel was partially submerged and had been abandoned.
The group has lodged a piracy complaint in the Netherlands against the captain and crew of a Japanese ship that collided with the Ady Gil.
"We have lodged a complaint of piracy with the Dutch prosecuting authority against the captain and crew of the Japanese vessel," Sea Shepherd legal representative Liesbeth Zegveld told AFP on Friday.
Prosecution spokeswoman Marieke van der Molen confirmed that a complaint had been received on Friday.
