According to ETH the acceptance rate this year was about 27 percent:

"Around 95% of ETH bachelor's students remain at ETH for their master’s degree, making up around two-thirds of the total number of master's students. The other third have gained their bachelor’s from a different institution, usually in another country. This autumn, some 900 new students from other universities will begin a master's degree at ETH Zurich. Overall, more than 3,300 young people applied for master's programmes – a new record."

https://www.ethz.ch/en/news-and-events/eth-news/news/2016/09/rising-number-of-students.html