"The European Union's insistence on keeping Hamas on the list of terrorist organisations is an immoral step, and reflects the EU's total bias in favour of the Israeli occupation," Hamas spokesman Sami Abu Zuhri told AFP.
"It provides it (Israel) with the cover for its crimes against the Palestinian people," he added.
Foreign ministers from the 28 EU member states decided at a Monday meeting to appeal the decision taken by the General Court of the European Union on December 17, the bloc's foreign policy chief Federica Mogherini said.
Israel, which slammed the December ruling, said it was not surprised about the EU's latest move.
"It's not a surprise, we're happy. We expected them to do this in the first place," a foreign ministry official said on condition of anonymity.
"We do expect that they will correct this procedural error that was identified," he added.
The ruling by the EU's second highest court had said that the blacklisting of Hamas in 2001 was based not on sound legal judgements but on conclusions derived from the media and the Internet.
Hamas, which has dominated the Gaza Strip since 2007, had appealed against its inclusion on the blacklist on several grounds.
Israel's closest ally the United States has urged the EU to keep up its sanctions on Hamas, saying the US position had "not changed" and Hamas is still a "designated foreign terrorist organisation".
The 50-day war last summer in which the Jewish state pounded Gaza with thousands of its strikes, killed nearly 2,200 Palestinians, mostly civilians, and 73 on the Israel side, mostly soldiers.