In this paper, we apply the extended triangular operational matrices of fractional order to solve the fractional voltrra model for population growth of a species in a closed system. The fractional derivative is considered in the Caputo sense. This technique is based on generalized operational matrix of triangular functions. The introduced method reduces the proposed problem for solving a system of algebraic equations. Illustrative examples are included to demonstrate the validity and the applicability of the proposed method../files/site1/files/61/9.pdf