The two communist countries remain ideological allies and have endorsed a similar transition to a market-oriented economy.
But their relationship evokes strong emotions and contradictions in Vietnam, where many bitterly recall 1,000 years of Chinese occupation and, more recently, a 1979 border war.
While the smaller nation has held onto many Chinese words, customs and traditions, it still feels a strong need to set itself apart from its giant neighbor.
The two countries share 10 of the zodiac calendar’s 12 signs– the rat, tiger, dragon, snake, horse, goat, monkey, rooster, dog and pig.
But the Vietnamese replace the rabbit with the cat and the ox with the buffalo.
Exactly why they opted for different animals remains unclear, but several scholars say the split can be traced back to the founding legends of the zodiac calendar.
One of these stories goes that Buddha invited animals to take part in a race across a river and the first 12 to reach the shore would have the honor of appearing on the calendar.
Unable to swim, close friends the cat and rat decided to hitch a ride on the ox’s back.
But as they approached the finish line, the two-faced rodent allegedly pushed the cat into the water — and the pair have been sworn enemies ever since.
The Vietnamese tell the tale somewhat differently.
According to them, it was the Jade Emperor, a Taoist god, who organized the race.
And in their version, the cat knows how to swim.
“There are anthropological and cultural explanations,” said Philippe Papin, an expert on Vietnamese history at the Ecole Pratique des Hautes Etudes in Paris.
But since many of today’s Vietnamese have Chinese origins, the most likely explanation lies in linguistics, he said.
“The Chinese word for rabbit is ‘mao’, which sounds like ‘meo’ in Vietnamese, where it means cat.
As the sound of the word changed, so did its meaning,” Papin said.
Regardless of how the split came about, the Vietnamese today have no interest in bringing their zodiac signs into line with the Middle Kingdom.
“For the Vietnamese, it’s a matter of national honour not to have copied China completely,” said Benoit de Treglode, from the Research Institute on Contemporary Southeast Asia in Bangkok.
“This form of distinction in imitation can be found throughout Vietnamese culture,” he added.
Politics play a role too with Beijing and Hanoi increasingly at odds over a number of long-running territorial disputes.
“We don’t know exactly how the selection of these 12 animals happened,” said Dao Thanh Huyen, an independent journalist based in Hanoi.
But “now that the words ‘China’ and ‘Chinese’ can become a source of controversy or even lead to arguments, many Vietnamese are happy not to be like their neighbor, even if it is fairly silly to take these things too seriously.”
Hoang Phat Trieu, a retired Vietnamese actor, says his compatriots simply prefer cats to rabbits.
“Most of the Vietnamese people are farmers,” the 76-year-old said.
“The rabbit has nothing to do with Vietnamese farmers, while the cat has always been a very good friend of farmers, trying to kill the rats that threaten their crops.”
As Vietnam marks its Tet Lunar New Year on Thursday, those born in the Years of the Rat, the Horse or the Rooster will be careful not to be the first to enter a house — as this is said to attract bad luck.
“This year is going to be an average year according to fortune tellers,” said Huyen.
But she hopes her husband and son, both Dogs in the zodiac calendar, will make the year more interesting than the disappointingly dull prediction.
“Everybody knows how cats and dogs get on,” she said, proving that the desire to make astrological predictions work in your favour is universal.
In that, at least, the Chinese and the Vietnamese are alike.