The Prime Minister has admitted that "not everything's perfect" on Britain's railways, particularly for strike beset commuters travelling on Southern Rail.
But she insisted rail travel is better under private rather than public ownership, despite fresh strikes hitting the network this week.
"I recognise that not everything's perfect and if you're on Southern railways, you almost certainly think that with all the strikes and disruptions that they have had," said May, speaking on the BBC's Andrew Marr Show on Sunday morning.
"But I can remember the days when the railways were nationalised and what people get today is a far better service than what they got on the nationalised railways."
She added that there is more investment under privatisation and greater reliability and that far more passengers are using the railways on more services.
"We do see a better service today," she said. "I can see that some people feel 'is this actually working for us', but it is a better system today."
Southern owner Govia Thameslink Railway (GTR) has said it is "aiming for business as usual" on most routes when workers of the RMT union walkout next week in two 24-hour strikes on Tuesday (3 October) and Thursday (5 October).