He told the Dutch newspaper Trouw in his interview.
"If later the majority of the Dutch vote "no", it will make the Netherlands less reliable partner", the newspaper quotes him as saying.
Van Rompuy noted that the government and parliament have already ratified the Association Agreement. According to him, the Netherlands became the only country that uses a similar procedure.
Van Rompuy also said that the tragic events on the Maidan Square in Kyiv city, and the war in the eastern Ukraine began since the Association Agreement and Ukraine is in need of support.
"Let's also not forget that the war has started with the Association Agreement. If you leave the situation as it had been before the Maidan, it will mean that these people died in vain. Because it is not so much an economic war, this war is about values. If we stop our backing, Ukraine will be lost," he said.
It was reported earlier, the Netherlands will vote in consultative referendum on the Association Agreement between EU-Ukraine on April 6.