His father was a merchant from Canton who traded with Batavia, but due to an accident he and his three sons Cai Yun蔡运, Cai Xuan蔡轩and Cai Gao蔡高had to pay off debts. Through the mediation of Rong Sande容三德who had taught Morrison Chinese in London already and who had returned to Canton, the three Cai brothers were hired by Morrison as servants in spring 1808, and the missionary demanded that they take part in the daily worship in his house. After half a year Cai Gao left Morrisons household, but he had started to pray Chinese prayers, and in 1810 he might have worked as printer for Morrison. Since Cai Xuan continued to serve Morrison, Cai Gao also kept close contact to Morrison, and in 1812 he began to express his faith experience in Chinese. In October 1812 Morrison wrote in his diary: „Cai Age makes progress, he prayed, and as I explained some prayers to him and knelt down to pray, he also knelt down and prayed.“ Cai Gao faithfully participated in the morning prayers, evening prayers and Sunday worship, and in June 1814 he wrote down his wish for forgiveness of sins and that he wanted to receive the Spirit. Although Rev. Morrison thought, Cai Gao had only a limited understanding of the faith, he still decided to baptize him. The baptism ceremony took place at a fountain near the coast at Macao on 16 July 1814. Cai Gao was the first Chinese Protestant Christian (Liang Fa梁发 was baptized in 1816.) In January 1817 there was a persecution, and Rong Sande, Cai Gao and Cai Xuan fled to Malacca. After half a year they returned to Canton, possibly they were not accustomed to the climate of Malacca. On 10 October 1818 Morrison noted down: „Cai Gao whom I baptized suffers from some serious lung ailment.“ According to the records of the London Missionary Society, Cai Gao died in October 1818. The brothers of Cai Gao kept contact to Morrison in the following years, and Cai Xuan asked for baptism in 1822, but it is not sure whether he was baptized.
