We investigated the effect of nanoscale C doping on the critical current density Jc and irreversibility field Birr of Fe-sheathed MgB2 tapes prepared by the in situ powder-in-tube method. The tapes were heat treated at 600-950 °C for 1h. Higher values of Jc and Birr were seen for 5at.% C-doped MgB2 tapes at higher sintering temperatures. The C-doped samples sintered at 950 °C showed the highest Birr, for example at 4.2K the Birr reached 22.9T. In particular, at 20K, Birr for the C-doped tape achieved 9T, which is comparable to the upper critical field of the commercial NbTi at 4.2K. This role of nanosized C particles can be very beneficial in the fabrication of MgB2 tapes for magnetic resonance imaging applications at 20K.