The Sarashina Diary (更級日記, Sarashina Nikki) is a memoir written by the daughter of Sugawara no Takasue, a lady-in-waiting of Heian-period Japan. Her work stands out for its descriptions of her travels and pilgrimages and is unique in the literature of the period, as well as one of the first in the genre of travel writing.

Takasue's daughter was a niece on her mother's side of Michitsuna's mother, author of another famous diary of the period, the Kagerō Nikki, whose personal name has also been lost. Other than the Sarashina Diary, she may also have authored Hamamatsu Chūnagon Monogatari, Mizukara kuyuru ('Self-reproach'), the Yoru no Nezame, and the Tale of Asakura.

This work is one of the six major literary memoirs/diaries written in the mid-Heian period, roughly from 900 to 1100. Lady Sarashina wrote her work with awareness of her distinguished lineage. She had a desire to produce something that would be worthy for her family line. This desire stemmed from her knowledge that autobiographical writing by women of her generation had achieved fame, which had assisted the writers' careers and their family lines. Her intention is evident in her text, as evidenced by careful editing.

Extracts from the work are part of Japanese high school students' classical Japanese studies.

Takasue's daughter, who was also known as 'Lady Sarashina', wrote her memoirs in her later years. She was born in 1008 and, in her childhood, travelled with her father, an assistant governor, to the provinces and, some years later, back to the capital. Her remembrances of the long, three-month journey back to the capital are unique in Heian literature, if terse and geographically inaccurate. Here she describes Mount Fuji, then an active volcano:

It has a most unusual shape and seems to have been painted deep blue; its thick cover of unmelting snow gives the impression that the mountain is wearing a white jacket over a dress of deep violet.

The Sarashina Diary recorded her life from the age of 12 to her fifties. Her memoirs start with her childhood days, when she delighted in reading tales, and prayed to be able to read the Tale of Genji from beginning to end. She records her joy when presented with a complete copy, and how she dreamed of living a romance like those described in it. When her life does not turn out as well as she had hoped, she blames her addiction to tales, which made her live in a fantasy world and neglect her spiritual growth. These records are impressive memories of Lady Sarashina's travel and dreams, and of her day-to-day life.

She spent her youth living at her father's house. In her thirties, she married Tachibana no Toshimichi, a government official, and from time to time seems to have served at court. At the end of her memoirs, she expresses her deep grief at her husband's death. Heian literature conventionally expresses sorrow at life's brevity, but Lady Sarashina conveys her pain and regret over the loss of those she has loved with passionate directness. She stopped writing at some time in her fifties, and no details about her own death are known.