Many problems such as the increase in the world population, global drought, and greenhouse gases have caused materials used in industries to be reconsidered. This is how the concept of green composite material emerged. Using natural fibers to obtain such materials is important in terms of sustainability. This study is aimed to use hemp fiber and banana fiber as natural fiber additives in the gypsum composite to produce green bio-composite. Natural fibers are chemically modified with 5% NaOH solution. In this way, a good fiber/matrix interface interaction is provided. The composite hardness test result of 5 wt% HB fiber added sample is obtained as 50.4. Compared to the control plaster sample test result, which is 53.6, a slight decrease can be seen. However, it is observed that the fibers held the structure together and sopped the crack propagation. The increase in the porous structure with fiber addition caused a decrease in the thermal conductivity of the composite. Comparing thermal conductivity result of 5 wt% HB fiber reinforced gypsum composite (0.131 W⸳mK-1) with respect to pure gypsum result (0.237 W⸳mK-1), it gave a promising result as an insulation material.