Mizhai biji 密齋筆記 "Notes from Secret Studio" is a "brush-notes"-style book (biji 筆記) written during the Southern Song period 宋 (960-1279) by Xie Caobo 謝采伯, courtesy name Yuanruo 元若, from Linhai 臨海 in the prefecture of Taizhou 臺州 (in today's Zhejiang province). He was a son of Chief Counsellor Xie Shenfu 謝深甫 (1139-1204) and the uncle of Empress Xie 謝皇后 (1210-1283) of Emperor Lizong 宋理宗 (r. 1224-1264). Xie obtained the jinshi degree in 1202 and was head of the military prefecture of Guangde 廣德軍, prefect of Huzhou 湖州, Vice Chamberlain, and then Chamberlain of the Court of Judicial Review (dalishi zheng 大理寺正).
At the age of sixty-three, he retired to the east, withdrew from public life, and devoted himself to reading books and historical texts. Whenever he had insights, he recorded them in writing. His studies spanned across the Classics, history, and various philosophical schools, drawing from a wide range of sources. He absorbed the literary discussions and artistic views of his contemporaries, accumulating knowledge day by day. Over time, he produced more this book of 5 juan length, with a supplement (Xuji 續記) of one fascicle.
The book makes frequent use of historical records, offering valuable reflections on gains and losses. It also includes various sayings and actions of earlier sages, often with underlying lessons or moral exhortations. Although some of his arguments are not fully refined, and his citations do not match the depth and breadth found in works like Rongzhai suibi 容齋隨筆 or Mengxi bitan 夢溪筆談, his writings have a solid foundation, with more virtues than flaws. As one of the best examples of Southern Song-era notes, novels, and historical writings, this work is highly valuable for reference and can also serve as a cautionary and instructive resource for future generations.
The original print, published by the author's son Xie Yimao 謝奕楙, is lost. The compilers of the imperial series Siku quanshu 四庫全書 retrieved the text from the Ming-period 明 (1368-1644) encyclopaedia Yongle dadian 永樂大典. It is also included in the series Yangsuxuan conglu 養素軒叢錄, Chicheng yishu huikan 赤城遺書彙刊. The series Linlang bishi congshu 琳瑯祕室叢書 enriches the text by criticial annotations by Hu Ting 胡珽 (the owner of the Linlang Studio) and Dong Jinjian 董金鑒. This edition is reproduced in the series Congshu jicheng chubian 叢書集成初編.