The work "Nhu Tay ky" (Records of the Nguyen Dynasty envoy in France) was a research work of Nguy Khac Dan during his envoy to France and Spain in June 1863. His work focuses on the study of French affairs. The main source used by Nguy Khac Dan to write Nhu Tay Ky is based on the account of Harmand, a Vietnamese-speaking French naval officer tasked with escorting envoys during their stay in France, combined with direct observation of the author himself. With a serious and scientific working attitude, Wei Khac Dan presented relatively fully and accurately on the cultural, political and economic aspects of France at that time.