Concerning to environmental protection, the reduction of nitrogen (N) excretion in animal production is required. In this paper, a computer model to predict the N excretion in growing-finishing cattle was developed and verified using the N intake and N content in the empty body which was based on the simulating equation of crude protein content in empty body weight (EBW). Furthermore, a minimal threshold of the N excretion was simulated for growing-finishing cattle with certain EBW and predicted average daily gain (ADG). This model would be valid for growing-finishing cattle of different breed types, frame sizes and sexes through the utilisation of equivalent EBW. Results of two trials on Italian growing-finishing steers were used to evaluate the computer model developed. The results showed that the simulated N (SN) content in empty body did not differ significantly with the real data; the simulated N excretion (SNE) was generally close to the actual N value when ADG predicted by metabolisable protein availability was similar to the real one (simulated: actual N excretion z0.8 on average). The application of this computer model is rather simple because it is possible to use the N intake and the difference of EBW during a certain period to predict N excretion. For environmental protection, minimal N excretion threshold could be used to decide the maximum number of growing-finishing cattle for a certain area.