Sailo (93) was rushed to the hospital at around 10 am and died there at 11.50 am after heart failure, its authorities said.
He is survived by wife Thansiami, sons, daughters and grandchildren.
Born on January 1, 1922, Sailo had joined the British Indian army in 1942 as a junior officer.
Mizo National Front (MNF) declared independence from the Union.
When he retired from the army in 1974, he had formed the Human Rights Committee to ease the lives of Mizo people reeling under insurgency and alleged army excesses.
Sailo had formed a political party called Mizoram Peoples Conference in April 17, 1975 and it won the Mizoram union territory elections in 1977 and he became the second chief minister of the state.
He was elected to the state assembly in 2008 for the last time and quit active politics at the age of 92 after his term ended in 2014.