Gadkari's sister Manisha, who is married to solar energy firm owner Kishore Totade, lives in the Pande Layout area of Nagpur where the incident took place yesterday.
Totade had gone to Kolkata for some work and was to return last afternoon when Manisha along with their son Shantanu went to the railway station to pick him up, police said.
Upon returning they found their flat had been broken into, and the burglars had made off with 81 tola of gold (approx one kg), two kg of silver and USD 1,000 in cash, they said.
Rana Pratap Nagar police are conducting further probe.
Nagpur, the state's second capital and the hometown of both Gadkari and Maharashtra Chief Minister Devendra Fadnavis, has seen a spate of crimes in the recent months. Earlier this week the government replaced the city police commissioner K K Pathak with S P Yadav.