Cable ducts of rail signalling equipment were set on fire in the states of Lower Saxony, Berlin, North Rhine-Westphalia and Saxony, police said.
"A political motive in relation to the G20 summit in Hamburg is not ruled out," they said in an appeal for eyewitnesses, AFP reported.
In all, 12 cases of arson were reported, with the perpetrators believed to have struck between 1 am (2300 GMT) and 4:30 am (0230 GMT).
Services in several locations including the eastern cities of Leipzig and Dresden as well as long-distance lines linking Berlin and Prague were disrupted, rail operator Deutsche Bahn said.
An anonymous claim of responsibility has been published on a far-left leaning website.
The group which called itself "Shutdown G20: take Hamburg offline!" said it had struck rail tracks which it described as "the central nervous system of capitalism".
Similar sabotage action hit Germany in 2011, believed to be carried out by leftist extremists then protesting against the German military's deployment in Afghanistan.
Germany hosts on July 7-8 a summit of the Group of 20 biggest economies in the northern city of Hamburg, with leaders including US President Donald Trump and Chinese leader Xi Jinping due to attend.