Sample preparation is a significant challenge for detection and sensing technologies, since the presence of blood cells can interfere with the accuracy and reliability of virus detection at the nanoscale for point-of-care testing. To the best of our knowledge, there is not an existing on-chip virus isolation technology that does not use complex fluidic pumps. Here, we presented a lab-on-a-chip filter device to isolate plasma and viruses from unprocessed whole blood based on size exclusion without using a micropump. We demonstrated that viruses (eg, HIV) can be separated on a filter-based chip (2-μm pore size) from HIV-spiked whole blood at high recovery efficiencies of 89.9% ± 5.0%, 80.5% ± 4.3%, and 78.2% ± 3.8%, for viral loads of 1000, 10,000 and 100,000 copies/mL, respectively. Meanwhile, 81.7% ± 6.7% of red blood cells and 89.5% ± 2.4% of white blood cells were retained on 2 μm pore-sized filter microchips. We also tested these filter microchips with seven HIV-infected patient samples and observed recovery efficiencies ranging from 73.1% ± 8.3% to 82.5% ± 4.1%. These results are first steps towards developing disposable point-of-care diagnostics and monitoring devices for resource-constrained settings, as well as hospital and primary care settings.