In this paper, a direct Landweber method is proposed to estimate on-line resistivity distribution of two-phase flows using electrical resistance tomography. The proposed method is formulated such that the iterative Landweber method is modified for on-line computation and the resistivity distribution is estimated directly by multiplying the measured data with a weighting matrix that is computed off-line. Moreover, to improve the reconstruction performance, adaptive step-lengths for the proposed method are computed. Numerical simulations and phantom experiments have been carried out to evaluate the performance of the proposed method.