5318 Dientzenhofer, provisional designation 1985 HG1, is a stony background asteroid from the inner regions of the asteroid belt, approximately 6 kilometers (3.7 miles) in diameter. It was discovered on 21 April 1985, by Czech astronomer Antonín Mrkos at the Kleť Observatory in Bohemia, Czech Republic. The transitional S-type asteroid has a rotation period of 8.06 hours. It was named after the German Baroque architects Christoph and Kilian Ignaz Dientzenhofer.
Dientzenhofer is a non-family asteroid of the main belt’s background population when applying the hierarchical clustering method to its proper orbital elements. Based on osculating Keplerian orbital elements, the asteroid has also been classified as a member of the Flora family (402), a giant asteroid family and the largest family of stony asteroids in the main-belt.
The asteroid orbits the Sun in the inner main-belt at a distance of 2.0–2.6 AU once every 3 years and 6 months (1,266 days; semi-major axis of 2.29 AU). Its orbit has an eccentricity of 0.13 and an inclination of 3° with respect to the ecliptic. The body’s observation arc begins with a precovery taken at Palomar Observatory in May 1971, or 14 years prior to its official discovery observation at Klet.
In 2016, two rotational lightcurves of Dientzenhofer were obtained from photometric observations by Italian astronomers at the Eurac Observatory (C62), Astronomical Observatory University of Siena (K54) and Carpione Observatory (K49). Lightcurve analysis gave an identical rotation period of 8.062 hours with a brightness amplitude of 0.70 and 0.84 magnitude, respectively (U=3-/3), indicative of a non-spheroidal shape.