The company said it expects to make 12 cents to 15 cents a share on revenue of between $395 million and $405 million for the full year.
Analysts had been looking for adjusted earnings of 19 cents a share on revenue of $402.9 million.
Shares of Zscaler fell $12.30, or 20% to $49.30 in after-hours trading.
For the just-completed quarter, Zscaler reported earnings of 7 cents a share on revenue of $86.11 million. Analysts had been looking for earnings of 1 cent a share, on sales of $82.8 million. In the same period a year ago, the company posted a loss of 1 cent a share on sales of $56.2 million. It reported a loss of $8.8 million.