Influenza A (H1N1) virus transmits person-to-person, posing a significant epidemic threat. In this work, we report the use of hydroxylated multi-walled carbon nanotubes (MWCNT-OH) as an ultrasensitive antibody-recognition-based immunosensor for the detection of the H1N1 hemagglutinin protein. Moreover, it is compared with a sensor based on the same carbon-based material graphene oxide (GO). To address the shortcomings of conventional three electrodes that are not suitable for portable carry-over testing. A screen-printed carbon electrode based on polyethylene terephthalate material is selected. It not only perfectly solves the above problem, but also significantly reduces the cost. Immunosensors detect immune responses using changes in electrical potential caused by specific reactions between antibodies and hemagglutinin proteins. The electrical signal is detected using differential pulse voltammetry and the limit of detection is calculated using the 3 N method. The results show that the MWCNT-OH immunosensor is highly sensitive and specific with a very low detection limit (0.058 fg/mL) and a good linear range (5 ~ 5×106 fg/mL). The detection limit (0.083 fg/mL) and linear range (50 ~ 5×105 fg/mL) of the GO immunosensor are slightly inferior to those of the MWCNT-OH immunosensor. This is due to MWCNT-OH´s larger surface area, pore volume, and defects, which provide more active sites. This suggests carbon nanotube-based sensors could be developed into practical clinical screening tools.