The lack of checks by conductors and ticket examiners since the start of the first lockdown in March last year has raised concerns about fare dodging and anti-social behaviour.
British Transport Police chiefs have expressed concern the resumption of checks could place staff at increased risk of assault and have urged them to wear body cameras.
The resumption of ticket checks and sales on trains is timed to coincide with the scrapping of travel restrictions across Scotland.
ScotRail hopes the presence of staff will cut anti-social behaviour and help keep trains clean and tidy.
It said its anti-fraud teams and British Transport Police (BTP) officers would also patrol trains to make spot checks on tickets.
They will be keen to maximise fare revenue after ScotRail said it had suffered a “massive financial downturn” by carrying just 10 per cent of normal passenger numbers.
Passengers must continue to wear face coverings and maintain 1m physical distancing.
ScotRail said it had seen a small increase in passenger numbers since travel restrictions were eased last Friday but it did not plan to expand the number of services until Sunday May 16, when they are due to rise to 82 per cent of normal with 90 per cent of seats.
It cut the number of services it runs to 65 per cent of normal in January, with 72 per cent of normal seats.
Head of customer operations Phil Campbell said: “The visible presence of ScotRail staff throughout trains is critically important for customers, and its return is a welcome step in the recovery of the railway.
“But it’s also vital our passengers remember they have a responsibility to each other, and our staff, to observe our rules for safer travel until Covid-19 restrictions are completely lifted.
“Customers are being reminded to buy tickets in advance of travel.
"It is a requirement to hold a valid ticket before boarding a train, and we will be increasing the frequency of our checks to make sure customers are playing their part.”
BTP chiefs have expressed fears about a “new culture” of some passengers travelling without tickets because of the lack of checks.
A BTP spokesperson said: “In anticipation of people returning to the railway, we will have an enhanced presence across the network to make sure those travelling are kept safe.
"Our officers will be on hand for reassurance and to remind passengers of the legal requirement to wear a face covering.
“Compliance with this law is high across the rail network, and we are confident passengers will want to play their part in protecting each other.
"But anyone who fails to comply without an exemption will be directed to leave the railway and can expect to receive a fixed penalty notice.”
Mick Hogg, Scottish organiser for the Rail, Maritime and Transport union, which represents conductors and ticket examiners, said: "Our number one priority is the safety of all staff and passengers, and adherence to the agreed risk assessment, which includes the fitting of a FFP2 mask.
"If staff are refused the fitting of a FFP2 mask by a competent person, they can refuse revenue protection on the grounds of safety.”