This means there are just four parties remaining. The Liberals had already left, and the Sweden Democrats and Left Party had been excluded from the start.
Christian Democrat party leader Ebba Busch Thor says they left over wanting "several billion" more in spending than the government's plans.
The Swedish Defence Minister was "noticably disappointed" by the Christian democrats' decision, reports TT. The minister says the party is "avoiding its responsibility." He would not say how big a gap there was between the money the Christian Democrats wanted, and what his own government, which is a coalition between the Greens and Social Democrats, was aiming for.
But the main opposition party, the Moderates, will stay in the defence talks. The party's defence spokesperson, Hans Wallmark, told news agency TT that his party wants to make sure of more money is set aside for defence by 2018, when there will be a new election.
If the Moderates and Center parties stay in the talks, the defence negotiations will include parties representing over two-thirds of the votes from the last election.