Big funding pledges from Germany, the UK and other nations to help war-torn Syrians are making an Australian pledge of $A25 million look tiny by comparison.
Foreign Minister Julie Bishop is to announce Australia's pledge at a Syria Donors Conference in London on Thursday.
German Chancellor Angela Merkel told the conference her country would pledge 1.1 billion euros ($A1.7 billion) in funding, with part of it covering half of the World Food Program's food provision for Syrian refugees this year.
She said that if all countries at the conference contributed their share it could be a "day of hope" for so many Syrians who had witnessed "terrible things" in their civil war.
British Prime Minister David Cameron called Germany's contribution "incredibly generous".
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He announced the UK would contribute STG510 million ($A1.04 billion) to the UN appeal for 2016 plus a further STG280 million for each of the next three years.
Other nations at the conference were also announcing big pledges that dwarfed Australia's.
In Australia, Labor and aid groups have described Canberra's pledge as far too small.
Opposition foreign affairs spokeswoman Tanya Plibersek said the government should scrap a "dumb plebiscite" on same-sex marriage and divert the $A160 million in savings to Syria as humanitarian assistance.
The $A25 million was "extraordinarily low" compared to the other countries' pledges, she said.
Oxfam Chief Executive Helen Szoke said Australia would be meeting less than 14 per cent of its fair share of funding for the Syria crisis for this year and she urged Ms Bishop to increase the amount.
"She knows the severity of the situation Syrian families are facing and we urge her to lead with her heart and up the ante for other donors at the conference," Dr Szoke said.
Aid group CARE Australia's Chief Executive Julia Newton-Howes said that when the UN was hoping to raise $A12.6 billion from international donors, it was "a drop in the bucket".
She said CARE was joining with other aid agencies to urge the government to provide $A178 million this year, a total deemed Australia's fair share.
But Ms Bishop has said Australia's aid response to the humanitarian crises in Syria and Iraq had been one of the largest ever, totalling $A230 million since 2011.
She said on top of that, Australia's military contribution to the coalition fighting the Islamic State group in Syria and Iraq cost around $A400 million this financial year.
Australia was also permanently resettling 12,000 Syrian refugees at a cost of around $830 million over four years.
"It has been one of our largest ever responses to a humanitarian crisis," she said in a statement before Thursday's conference.
She was also to announce the deployment of 10 Australian water, sanitation, education and other specialists to Jordan and the Lebanon to assist Syrian refugees.
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