Mining-induced microseismicity has been extensively used to evaluate the potential for rock bursts and coal and gas outbursts in underground coal mines. In a research project completed a few years ago, it was observed that characteristics of microseismicity around a longwall working panel were fairly consistent over the monitoring period until a heterogeneous zone with a relatively high coal strength was reached. The current research presented in this paper aims at achieving a better understanding of the effect of heterogeneity on microseismic activity in longwall coal mining. A microseismicity modelling approach which combines deterministic stress and failure analysis together with a stochastic fracture slip evaluation was used to simulate the evolution of microseismicity induced by the progressive face advance passing through a heterogeneous zone. The heterogeneous zone was taken into account by varying the material strength of the elements within the high strength zone and the fracture attributes within this zone. Results have shown that both the high rock strength of coal lithotype and low fracture intensity within this zone contribute to the decrease in seismic event counts, and that the increase in energy released results from the combined effects of increased stress drops and slipped fracture sizes when the high strength zone is approached.