The Ukrainian government collapsed in September after Yushchenko's party pulled out in protest at Tymoshenko's decision to support an attempt by the pro-Russian opposition to reduce the powers held by the president.
At that time, Yushchenko accused Tymoshenko of ignoring national interests for the sake of gaining power.
"I am deeply convinced that it was human ambition that destroyed the democratic coalition - one person's ambition, lust for power, differences in values and putting personal interests ahead of national ones," Yushchenko said in reference to Tymoshenko on Wednesday, as he dissolved parliament.
Tensions between the two leaders had deteriorated after Yushchenko voiced his support for Georgia during its war with Russia in August.
Yushchenko and Tymoshenko are expected to contest the presidency in 2009 or early 2010.