In the recovery section of pulp and paper mill the smelt from the furnace is dissolved in water, the green coloured is called as green liquor. The green liquor obtained from paper mills using agricultural residues as raw material contains silica. This silica interferes in every stage of recovery section. Desilication of green liquor is essential as it restricts silica entry into the downstream units and silica re-entry through recovered and recycled digester chemicals. In present work, multi layer perceptron (MLP) ANN with GDR based learning have been developed for estimation of silica concentration and degree of desilication as a function of pH and time. The numbers of neurons and hidden layers were varied to act the most accurate ANN model. The ANN models thus developed with three hidden layers were found to be of good accuracy level, both for training and test data set.