If an insured driver driving an uninsured car hits another car is his insurance responsible?

Probably. Maybe. Maybe Not. Better ask your agent. If the uninsured car does not belong to the driver and he does not have regular use of it, most policies will cover the accident. Also if he just (within the past couple of days) purchased the car, he should be OK. If the driver owns the vehicle or uses it on a regular basis, the company will probably pay and terminate his coverage. Probably. Maybe. Maybe Not. Better ask your agent. If the uninsured car does not belong to the driver and he does not have regular use of it, most policies will cover the accident. Also if he just (within the past couple of days) purchased the car, he should be OK. If the driver owns the vehicle or uses it on a regular basis, the company will probably pay and terminate his coverage.