Former king Norodom Sihanouk, wife Monineath and son King Sihamoni flew to Beijing for Wednesday, after a farewell from many high-ranking officials at Phnom Penh International Airport.
King Sihamoni was expected to return after two weeks, though Sihanouk and Monineath will stay for medical care.
The absence of the former king ahead of national elections was a minor concern for some political observers.
"The times when the king, especially former king Sihanouk, stays in the country, it seems warmer and there seem to be fewer political conflicts," said Thun Saray, director of the human rights organization Adhoc.
"When he leaves, we also feel cold, but it is not too bad a worry," said opposition leader Sam Rainsy.
Government spokesman Khieu Kanharith attributed Cambodia's "poltical stability" to Prime Minister Hun Sen's "broad leadership," and said even without the king, "there is also political stability."
