Four hundred couples entered the pre-Valentine's Day sweepstakes organised by two gay rights charities and the internet giant in what is a highly unusual move for China where same-sex marriage is illegal and homosexuality remains a taboo subject.
The hopefuls had to upload a short video explaining their love story. The organisers then whittled down the field to just 20 finalists before opening the competition to a public vote.
The unions will not be recognised under Chinese law but an Alibaba spokeswoman described the move as "more of a symbolic kind of gesture".
"It will strengthen awareness and encourage respect and tolerance towards homosexuality," the company said.
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Beijing only decriminalised homosexuality in 1997 and stopped classifying it as a mental illness in 2011.
Gay rights campaigners in China still face harassment from authorities or bureaucratic roadblocks.
LGBT groups in China are barred from registering as official non-governmental organisations (NGOs), and activists often take a low-profile approach to promoting events lest the authorities decide to crack down.
The competition was part of promotion Taobao's new travel platform aimed at the gay community with deals on trips to "destinations were gay marriage is legal" including the United States, New Zealand and Canada.