Fujiwara no Mototsune (藤原 基経?, 836 – February 25, 891), also known as Horikawa Daijin, was a statesman, courtier and politician.
Mototsune continued the trend begun by Yoshifusa of monopolizing the position of regent to the Japanese emperor. He was third son of Fujiwara no Nagayoshi, brother of Yoshifusa, and Fujiwara no Otoharu (藤原 乙春), daughter of Fujiwara no Tsugutada. He was adopted by Yoshifusa who had no sons, and Mototsune followed in Yoshifusa's footsteps.
After the emperor had reached his maturity, however, Mototsune invented the position of kampaku regent for himself. This innovation allowed the Fujiwara clan to tighten its grip on power right throughout an emperor's reign.
Mototsune is referred to as Shōsen Kō (昭宣公) (posthumous name as Daijō Daijin).