Net loss was T$1.88 billion ($62.06 million) in January-March, compared with a mean loss of T$1.59 billion estimated by 18 analysts polled by Reuters.
The result also compared with a profit of T$300 million in the previous quarter - largely attributed to the sale of a stake in headphone maker Beats Electronics LLC - and profit of T$85 million a year earlier.
Shares of HTC closed 3.57 percent higher on Monday ahead of the earnings release, compared with a 0.14 percent decline in the benchmark index.