(20161) 1996 TR66

 is a trans-Neptunian object orbiting beyond Pluto in the Kuiper belt of the outermost Solar System, approximately 139 km in diameter. It was discovered on 8 October 1996, by astronomers David Jewitt, Chad Trujillo, Jane Luu, and Jun Chen at the Mauna Kea Observatory, Hawaii, in the United States. It was the first discovery of a twotino.

Orbit and classification
It orbits the Sun at a distance of 28.6–66.6 AU once every 328 years and 8 months (120,032 days). Its orbit has an eccentricity of 0.40 and an inclination of 12° with respect to the ecliptic. Near perihelion, it comes closer to the Sun than Neptune does (29.7 AU). It has a semi-major axis (average distance from the Sun) near the edge of the classical belt.

Twotino
was the first twotino discovered. Twotinos stay in a 1:2 orbital resonance with Neptune, which means that for every one orbit a twotino makes, Neptune orbits two times. Both the Minor Planet Center and the Deep Ecliptic Survey list this trans-Neptunian object as a twotino.

Numbering and naming
This minor planet was numbered by the Minor Planet Center on 9 January 2001. As of 2018, it has not been named.