Juanda airport opened at 9 am (0200 GMT) after nearly 20 hours of closure, the Transport Ministry said.
"But it's conditional and there is the possibility that volcanic ash could halt air traffic again," a spokeswoman for the airport operator was quoted by state news agency Antara.
Juanda and three other airports in Jember, Banyuwangi and Sumenep in East Java were closed after the province's Mount Raung ejected ash and debris in its latest eruption.
An earlier eruption last week caused the closure of five airports including Ngurah Rai in Bali.
Another airport was closed in North Maluku, Ternate on the eastern part of the country, due to a eruption of Mount Gamalama that ejected ash up to 1,500 metres into the air early Thursday.
The airports' closure came as millions of people in Muslim-majority Indonesia were travelling to their home towns to celebrate Eid, which marks the end of the Muslim holy month of fasting.
The Transport Ministry has increased land transport for travellers whose flights were cancelled by the airport closures.