Constant Pierre-Joseph De Deken is a Belgian colonial explorer, anthropologist and Roman Catholic missionary.
The son of Ludovicus De Deken and Maria-Theresia Van Dyck, he studied theology at the major seminary of Mechelen, then he made his novitiate in Scheut Fathers in 1877. There became ordained priest in June 1879 and took his final vows in March 1881 to be called to go to China to evangelize the population. He is sent to the Apostolic Vicariate of Kan-Su-Koukounor (now Gansu) in Chinese Turkestan. Scheutistes are present in China since 1865 and want to expand their ministry to the northwest. There follows a short study period Lanchow to improve his Chinese and evangelizing the region of Sichuan from April 1882, he toured from the parish of Kuldja. He remained there until 1889.
In 1889 he joined a scientific expedition of Bonvalot Gabriel (accompanied by Prince Henri d'Orléans, as botanist and photographer) in Turkestan with his Chinese servant Bartholomeus. De Deken speaks Chinese and serves as interpreter. The goal was to reach Shanghai across the Central Asia, Tibetan and the Tonkin, which was completed in September 1890. De Deken then separates from the explorers and heads on a boat to Haiphong to eventually return to France. These were the first modern European explorations penetrating the high Tibetan plateau, away from the roads which had been done before the Father Huc and later Nikolai Przewalski. This expedition was unprecedented, having traveled six thousand kilometers and recovering botanical collections that were subsequently studied at the Natural History Museum of Paris. A year later Father De Deken left China and returned to the Scheutist fathers in Brussels for a year. He published a description of his journey in a book published in French entitled Across Asia (1891).
De Deken left Belgium in June 1892, this time to king Leopold's domain: Congo Free State, where Scheutists are present since 1889. There he was appointed to Boma. From autumn 1894 to autumn 1895, he returned to Brussels. His health began failing. Subsequently, he returned to the Congo, where he arrived in November 1895 and died 3 March 1896 a few days before celebrating his forty-four years.