No fighting was reported overnight after the deal was struck in Minsk, capital of Belarus, on Friday.
Ukraine`s President Petro Poroshenko says there should now be talks about a long-term solution to the conflict, which has killed about 2,600 people.
However, the rebels said the ceasefire had not changed their policy of wanting to separate from Ukraine.
The ceasefire talks, brokered by the Organization for Security and Co-operation in Europe (OSCE), involved former Ukrainian President Leonid Kuchma, leaders of the pro-Russian rebels, and Russian Ambassador to Ukraine Mikhail Zurabov.
The OSCE said it would monitor the ceasefire.