WELLINGTON, New Zealand--Infant formula and fresh milk marketing company a2 Milk Company Ltd. said its full-year earnings increased by more than a third due to strong demand in China.

Net profit for the 12 months ended June 30 was 385.8 million New Zealand dollars ($253 million), up 34.1% from the previous year, a2 Milk Company said Wednesday. Revenue rose 32.8% to NZ$1.73 billion.

The company said its profit margin for the year was 31.7%. It had forecast revenue of NZ$1.7 billion to NZ$1.75 billion and a profit margin of 31% to 32%.

Write to Stephen Wright at stephen.wright@wsj.com