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Louis Thollon (May 2, 1829 – April 8, 1887) was a French astronomer.
He was born in Ambronay, France. Beginning in 1881, Thollon joined the staff of the new Nice Observatory where he undertook a long-term observation program of the Sun using a spectroscope of his own design. In the process, he recorded a solar spectrum consisting of 3,000 absorption lines in the optical band.
In 1882, he joined André Puiseux on an expedition to Egypt to observe the solar eclipse on May 17. The same year he traveled to Portugal to watch the Venus transit, but met with disappointment. During the 1886 Mars opposition, he assisted the observatory director, Henri Perrotin, in observing the planet with a 15 in (38 cm) reflecting telescope. Both men reported that they spotted canali on the surface of the planet, apparently confirming the 1877 discovery of these features by Italian astronomer Giovanni Schiaparelli. Thollon died in Lyon, France.