Amazon has the second-largest market capitalization of any company in the world (about $918 billion as of this writing), after briefly breaking the trillion-dollar mark last year.

But it also has something immensely valuable: the most valuable brand of any company in the world.

According to a study by WPP research agency Kantar released Thursday, Amazon's brand alone is now worth $315.5 billion, which is 52 percent more than it was a year ago, and enough to vault it over Apple ($309.5 billion) and Google ($309 billion) in the annual rankings.

Either Apple or Google had been in the top position in the BrandZ Top 100 Most Valuable Global Brand ranking for the past 12 years, until now.

So, why is Amazon's brand suddenly worth so much more? According to the study, it's due to:

  • "Smart acquisitions, that have led to new revenue streams" 
  • "Excellent customer service provision" 
  • "Its ability to stay ahead of its competitors by offering a diverse ecosystem of products and services"

Among those acquisitions: self-driving car and truck platforms, plus its $753 million acquisition of PillPack and its $575 million investment in London-based delivery service Deliveroo. 

"Amazon's phenomenal brand value growth of almost $108 billion in the past year demonstrates how brands are now less anchored to individual categories and regions," Doreen Wang, Kantar's global head of BrandZ, said in a statement emailed to CNBC.

Microsoft, which has the largest market capitalization at the moment, came in fourth in the rankings with a brand worth $251.2 billion, according to the study. Here's the list of the top 10:

1.    Amazon, $315.505 billion
2.    Apple, $309.527 billion
3.    Google, $309 billion
4.    Microsoft, $251.244 billion
5.    Visa, $177.918 billion
6.    Facebook, $158.968 billion
7.    Alibaba, $131.246 billion
8.    Tencent, $130.862 billion
9.    McDonald's, $130.368 billion
10.  AT&T, $108.375 billion

Plus, a few others of interest: 

15.    Marlboro, $71.958 billion
17.    Disney, $57.007 billion
21.    Nike, $47.360 billion
24.    Starbucks, $45.884 billion
32.    Walmart, $36.801 billion
34.    Netflix, $34.290 billion
58.    LinkedIn, $22.816 billion
76.    Ikea, $18.949 billion
100.  Adidas, $13.355 billion

You can find more information here, and a link to the entire study here. (Be forewarned: It's a 388-page online document.)