Two novel hyperbranched donor-acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core (4BrCzP1 and 4BrCzP2) were synthesized and characterized. The third order nonlinear optical properties of the materials were studied using Z-scan technique with femtosecond Ti: sapphire laser with delivering pulses of 140 fs at 800 nm. The nonlinear optical refractive index was 9.29 x 10(-8) esu for 4BrCzP1 and 3.19 x 10(-7) esu for 4BrCzP2, respectively. While the third order nonlinear susceptibility was 1.29 x 10(-8) esu for 4BrCzP1 and 4.33 x 10(-8) esu for 4BrCzP2, respectively. The experimental results indicated that the hyperbranched polyfluorenes was a promising candidate in the application of third order nonlinear optical materials. (C) 2013 Elsevier Ltd. All rights reserved.