"The Offer significantly undervalues future cash flows to AGL of operating the Liddell Power Station until 2022 and the repurposing of the site thereafter," the company said in a statement.
Chinese-owned Alinta Energy had made an unsolicited bid for the ageing plant in April, amid a national debate in Australia over energy security in the country stemming from a projected supply shortfall in the near future.
AGL had come under pressure from Australia's prime minister either to sell the plant or keep it running beyond 2022, following a string of blackouts and price spikes.
The company said it would continue its plan of shifting to gas and renewable power plants as part of a phased exit from coal.
AGL had said it planned to build an A$400 million gas-fired power plant in New South Wales as part of the plan, which would bridge a possible supply shortage for when its Liddell power station shuts.
($1 = 1.3291 Australian dollars)