The preliminary results suggest voters in the Netherlands have rejected this trade deal. According to media reports, with 99.8% of the votes counted, 61.1% had said "No", with 38% supporting a deal. Turnout is projected at 32%, above the 30% threshold of voters needed to be valid but within a 3% margin of error.
The Dutch parliament has already ratified the EU agreement and the result of the vote is not binding. Prime Minister Mark Rutte said his government may have to reconsider the treaty if the vote is valid. His view is if the turnout is more than 30%, with such a victory for the ´No´ camp, ratification cannot go ahead without discussion.
"We will have to wait and see but it is clear that the ´No´ voters won convincingly. The question is whether or not the required turnout will be met." Mr Rutte said in a televised reaction.
The vote was seen as a test of public opinion towards the EU, and observers said many voters were likely to use the referendum as a chance to protest against the EU´s expansion and what they consider to be its undemocratic decision-making processes.
Dutch voters to express frustration at the EU
Under the 2015 Dutch law that created advisory referendums, the result will be considered valid only if turnout is higher than 30%
Officially The Netherlands has rejected a landmark deal between the EU and Ukraine - in reality the issues that dominated this campaign were much wider.
The referendum was triggered by the Eurosceptic movement which used a new Dutch law designed to promote democracy to force a vote by gathering enough signatures on a petition.
From the start activists said this was a chance for Dutch voters to express frustration at the EU, in particular what they see as its desire to expand despite democratic shortcomings.
But they were not asked to simply pass judgment on the EU, and throughout the campaign those promoting a Yes vote were frustrated by what they saw as attempts by Eurosceptics to hijack a debate which should have been about relations between Ukraine, Russia and Europe.
Some say the multiple layers to this referendum means the result cannot seen as a true reflection of the scale of Dutch Euroscepticism. Nonetheless, the rejection of this deal will rattle the nerves of European leaders who are already struggling to maintain unity in the face of economic instability and the migrant crisis.