A new and unusual nightside auroral distortion was detected around 1400 UT on 11 December 2004 by TIMED/GUVI (northern hemisphere) and IMAGE/FUV (southern hemisphere). The distortion has a special "tongue" shape (possibly a special auroral streamer) and is called the Nightside Auroral Tongue (NAT) hereafter. We found that the NAT is a conjugate phenomenon. The NAT consists of both diffuse aurora and nearly north-south arcs. The NAT extended from ~72¿ Mlat to 62¿ Mlat in the 0100 MLT sector, well beyond the proton isotropic boundary (b2i) around 66¿ Mlat. The width of the NAT varies from 2 hour in MLT at magnetic latitude around 70¿ to 0.5 hour in MLT at Mlat < 65¿. The width of the arcs within the NAT is only about 30 km on average. The observed unusual feature of NAT is associated with a strong IP shock and a large solar wind electric field.