A simulation model was developed to estimate the areal (surface) deposition pattern of 129mTe after the Fukushima Daiichi nuclear power plant (FDNPP) accident. Using this model, the timing and intensity of the 129mTe release were reverse estimated from the environmental monitoring data. Validation using 137Cs data showed that the model simulated atmospheric dispersion and estimated surface deposition with relatively high accuracy. The estimated surface deposition pattern of 129mTe was consistent with the actual measured pattern. The estimated time and activity of 129mTe emissions indicated that 129mTe was predominantly emitted from FDNPP Unit 3.