China Railway Construction has raised 22.25bn yuan ($3.1bn; $1.6bn) by selling shares on the Shanghai Stock Exchange.
The state-owned firm, which built the first rail link to Tibet said the share sale was hugely oversubscribed.
That was despite recent stock market volatility and a 30% slump in Chinese shares since last October.
But China Railway Construction is attractive because it is closely tied to China's booming economic growth.
Safe haven?
Beijing has set aside $175bn in its current budget to invest in railways.
Analysts also said that shares were being sold at a discount to the firm's main rival China Railway Group.
In December it raised $5.5bn in a share sale and shares have jumped 62% in Hong Kong.
The flotation of China Railway Construction is likely to be the biggest share sale of the year, but could be trumped by credit card company Visa, which hopes to raise $18bn.
