Xiaomi launched mi.Com in France, Britain and Germany on today, it said in a statement.
The store went online in the United States yesterday, it added.
Xiaomi, which was only founded in 2010 by entrepreneur Lei Jun, has excelled in China's cut-throat smartphone market by delivering high-performance products at low prices.
In just five years, the Chinese firm has become the world's number three smartphone vendor, behind only Apple and South Korea's Samsung, with rapid growth in emerging countries.
A company spokeswoman told AFP on today that the site is restricted to accessories.
Products on offer include a USD 14.99 fitness band compared with USD 99.99 for the mid-range tracker from San Francisco-based Jawbone, USD 79.99 headphones and battery cells as cheap as USD 9.99, according to the website.
Shipments are currently limited to the four countries, the company said.
However, Xiaomi has signalled its intention to offer more products to consumers in the US and Europe.
It has enjoyed huge success in its home market of China, and in the first quarter of 2015 held a 13.7 per cent market share - behind only US rival Apple.
It was the top smartphone company in China during 2014, claiming sales of more than 61 million smartphones, up 227 percent from 2013.
Xiaomi has launched products outside mainland China in Hong Kong and Taiwan, as well as southeast Asia, but has yet to expand its footprint into developed countries.
Hugo Barra, vice president of Xiaomi Global, said in the statement he was "truly excited to bring a selection of our best-selling accessories" to consumers in the West.