The objectives of this thesis is to study critically lives of seventy-three Bhikkhunis and their enlightenment as exposed in the Therigatha. The result of the study is as follows :- Their enlightenment was related to two main backgrounds, namely; the background of their previous births and that of the present ones. Of these the former suggests that they all, before the enlightenment, had an audience with the past Buddha by listening to their sermons, taking vows in the their presence to attain Nibbana and continually accumulated merits such as giving alms etc. The letter suggests that their differences of family, education and habit was not hindrance to their enlightenment. For practical approaches to their enlightenment, they attained Nibbana through the two techniques, namely : the Tranquility (Samatha) Mental Development and the Insight (Vipassana) One. These two depend on each other. In some cases the Tranquility Mental Development led the Insight one. Sometimes the Insight led the Tranquility. But at the end they functions together to get rid of mental defilements. From my research, seventy-two of them attained Nibbana through the Tranquility Mental Development leading the Insight One, Only one through the Insight mental Development leading the Tranquility One. Finally, however, they all realized by themselves after their enlightenment that Finished is birth, live is pure life, what should be done is done, nothing more is left to be done.