Abstract： Objective To compare the dosimetric differences of permanent prostate braehytherapy utilizing 131Cs,125 I and 103 Pd seeds.Methods Twenty-five patients with T1-T2c prostate cancer who had previously implanted with 125I seeds were randomly selected in our study.The patients were re-planned with 131 Cs,125 I and 103 Pd seeds by using the Prowess Brachytherpay 3.1 planning system to the prescription doses of 115 Gy,145 Gy and 125 Gy,respectively.The seed strengths were 1.8 U,0.5 U and 1.8 U,respeetively. The prostate,prostatic urethra and anterior wall of the rectum were contoured on trans-rectal ultrasound ima ges.PTV was outlined based on the prostate volume with no margin applied.The attempted planning goals were that V100(tbe percentage volume of the prostate receiving at least 100% of the prescription doses)= 95%,D90 (the minimum percentage dose covering 90% of the prostate volume) ≥100% ,and prostatic ure thra UD10 (the maximum percentage dose receiving by 10% of the contoured urethra)≤150%.For the plan comparison,we also computed prostate V150,prostatic urethra UV120,rectum RV100,and the number of implan ted seeds and needles.The significance of the differences was tested using one way analysis of variance. Results The average V200 in the 103pd,125 I and 131 Cs plans were 28.7% ,20.9% and 19.6% (F=42.50, P =0.000) ;the average V150 were 51.9% ,42.1% and 39.4% (F=26.15,P =0.000) ;the average UV120 were 26.9% ,29.5% and 23.8% (F = 0.37,P =0.691) ; and the average rectum RV100 were 0.31 cm3, 0.22 cm3 and 0.19 cm3(F=0.43,P=0.652).For 103 Pd,124 I and 131 Cs,the average number of implanted seeds per cm3 prostate were 2.02,2.01 and 1.87(F = 1.92 ,P =0.154) ,and the average number of needles were 33.6,32.9 and 31.6(F=0.26,P=0.772). Conclusions Comparing to 124 I and 103 pd seeds used in permanent prostate brachytherapy ,131 Cs seeds has better dose homogeneity,and possible better sparing of the urethra and rectum,with comparable or less implanted seeds and needles.