The provision is part of a new anti-cybercrime law which came into force last week
Saudi Arabia on Monday announced "spying" on your spouse's phone is now a criminal offence potentially punishable by a hefty fine - and a year in jail.
"Married individuals planning to spy on their spouse in Saudi Arabia will need to think twice, because such an activity could potentially attract a fine of 500,000 riyals ($133,000, 108,000 euros), along with a prison term for a year," read an English-language statement released by Saudi Arabia's information ministry.
The provision, part of a new anti-cybercrime law which came into force last week, is meant to "protect morals of individuals and society and protect privacy", the ministry said.
The move comes amid a "steady increase in cybercrimes such as blackmail, embezzlement and defamation", the statement said.
The ultra-conservative kingdom is among the world's top per capita users of cellphone apps and social media.
More than half of Saudi Arabia's citizens are under 25, many of whom spend much of their time on mobile platforms, away from official strictures and traditions.
Saudi Arabia has launched a string of highly-publicised policy changes since the rise of Crown Prince Mohammed bin Salman to power last year.
The country will allow women to drive as of June and has lifted a decades-long ban on cinemas.
Saudi Arabia's legislation on cybercrime has drawn harsh criticism from international rights groups in the past.
Dozens of Saudi citizens have been convicted on charges linked to dissent under a previous sweeping law, particularly linked to posts on Twitter.
Last September, authorities issued a public call for citizens to report on the social media activities of their fellow citizens, under a broad definition of "terrorist" crimes.
It directed suspicious activity be reported via the government-run "We are all security" app.