The conflict between Saudi-backed forces loyal to fugitive former President Abd-Rabbu Mansour Hadi and the rival Houthis movement has killed more than 6,200 people and triggered a humanitarian crisis in one of the Arab world's poorest countries.
The truce from Sunday midnight (2100 GMT) precedes peace talks on April 18 in Kuwait.
A spokesman for a Saudi-led military coalition, which has been carrying out airstrikes over the past year, urged the Houthis to respect the agreement which he said the Hadi loyalists and the coalition would adhere to.
"But if there is any violation of this ceasefire, we will have the right to retaliate, to assess the situation at that time and take whatever steps are necessary to stop these violations," Ahmed al-Asiri told the Reuters news agency by telephone.
He said military officials loyal to Hadi and some Houthi represantatives had met over the past two days in southern Saudi Arabia to prepare for the ceasefire and had signed agreements on how it would be implemented and monitored.
The rival sides had formed committees to observe the halt in hostilities and facilitate the delivery of humanitarian aid, he said.
A spokesman for the Houthis and their allies said they were also committed to the truce but also retained the right to respond if it was broken by the other side.
Hours before the fighting was due to stop, heavy battles flared between forces loyal to Hadi and Houthi fighters in al-Maton, north of Sana'a, residents said.