There are provided a microorganism characterized by producing poly-.gamma.-L-glutamate with a molecular weight of 1,300,000 or greater and uniform optical purity under liquid culture conditions, a method of screening for the microorganism, a method of producing poly-.gamma.-L-glutamate having large molecular weight by using the microorganism, and poly-.gamma.-L-glutamate having an average molecular weight of 1,300,000 or greater. In addition, usages of these are provided.