Four-year-old giant panda twins Ryuhin and Shuhin came home in southwest China on Sunday from their birthplace Japan.

The two male pandas left the Adventure World Park Zoo in western Japan's Wakayama prefecture early Saturday morning and arrived at the Chengdu Research Base of Giant Panda Breeding Sunday afternoon by way of Osaka of Japan and Beijing.

The panda twins enjoyed a smooth trip, both keeping quiet and in good health on homebound trip, accompanied by panda fans, experts, government officials and media staff from Japan and China, said Huang Xiangming,curator of the Animal Management Department with the base.

The twins received a warm welcome at a special ceremony held at the research base, witnessed by hundreds of panda fans and tourists from home and abroad.

Huang said the pandas would be quarantined in a newly-built house at the base for two to three months, when they will enjoy a quiet environment and adapt themselves to the new diet before meeting visitors.

"Then they'll receive sex education, which includes more communication with female pandas and watching adult pandas mating, " said Huang. "We'll let them join our breeding plan in two to three years, when they grow up."

Koji Imazu, head of the animal management department with the Adventure World Park Zoo, said it was an honorable event to send the panda twins home this year, which marking the 35th anniversary of the normalization of Sino-Japanese relations.

"Our staff and people of Wakayama as well as all panda fans in Japan are looking forward to the birth of the twins' own babies," said Imazu. "We hope they'll link Chinese and Japanese together and strengthen our friendship."

"I was regretful and lonely after learning that Ryuhin and Shuhin had to leave us," said Tanaka Kojo, head of the Panda Protection Institute of Japan, who accompanied the twins back to China. "But I feel comfort and happy now that they've received such a warm welcome in Chengdu at home."

The pair were born on Sept. 8, 2003, to Yong Ming and Mei Mei, which the Chengdu research base leased to the Adventure World Park Zoo in 1994 and 2000 respectively under a Sino-Japanese cooperation program on giant panda breeding.

The Chinese government has launched long-term cooperation on giant panda breeding with Japan, the United States and Spain since 1994. Twenty-five pandas have been leased to the countries.

According to cooperation agreement, cubs born overseas by pandas on loan belong to China and should be returned to China after they become sexually mature or the cooperation ends.

Giant pandas are one of the most endangered species in the world. There are only 1,590 giant pandas living in the wild, most of them in southwest China's mountainous regions.

By the end of 2006, about 210 giant pandas lived in captivity in China.(Source: Xinhua )