Taira no Tadatsune (平 忠常, October 19, 975? - June 28, 1031) was a chieftain of the Taira clan in the early 11th century, and predecessor of the Chiba clan. He was also, for a time, Governor of Shimōsa and Vice-Governor of Kazusa Provinces, and manager of the Grand Shrine of Ise in fact if not in name.
In 1028, Tadatsune resigned from the office of Vice-Governor of Kazusa, and attacked Kazusa and Awa Provinces, seeking to expand his power base. The Imperial Court sought to stop him, and nominated Minamoto no Yorinobu, Governor of Ise Province, to lead the attack; he refused. The Court then appointed Taira no Naokata and Nakahara Narimichi, who were recalled soon afterwards, after making no progress. The Governor of Awa Province fled to Kyoto in 1030, and the following year, Minamoto no Yorinobu rose to the occasion, after being appointed Governor of Kai Province.
Knowing he could not defeat Yorinobu, Tadatsune surrendered without a fight, and was taken prisoner, perishing on the way to the capital.