Objective To calibrate and assess the dose distribution of 125 I seed brachytherapy. Methods Twenty 125 I seeds, each with activity of 12.2 MBq, were implanted on the circumference of a circle 15mm across in a phantom. Into a designed prostate model, 70 125 I seeds were implanted in four planes. The absorbed dose rate of the target volume was monitored by Farmar 2570 dosimeter and thermoluminescence dosimeters (TLD) with the isodose curves drawn on Kodak films. Results The central dose rates of the circular target volume assessed by Farmar 2570 and TLD were 8.4, 7.9 cGy/h in the phantom and 12.0, 11.1 cGy/h in the prostate model. For the target volume of the prostate model, the total absorbed dose was 24?219 cGy. The dose rate 4 cm from the prostate cancer as shown by the isodose curves was only 10% of the central dose rate. Conclusion The central dose rate of target volume measured by the two methods are similar.