CaproF is a biodegradable subcutaneous contraceptive implant of releasing levonorgestrel (LNG), which is expected to provide an effective contraception for 2 years. This study was undertaken to assess the one year preliminary clinical results of using CaproF in 19 subjects. All subjects (n=19) completed the 1 year study, and the contraceptive effectiveness and follow up rate were both 100%. The incidence of side effects was low. The major side effects were menstrual disorder, but bleeding patterns tended to be improved and restored to be the same as pre implantation ones with time. There were no significant increase in weight (P>0.05) and no changes in blood pressure. In the 3 rd , 6 th and 12 th months after using CaproF, the cervical mucus became scanty and viscous without fern like crystals. The amount of menstrual blood loss decreased from 49.38 ml of pre implantation to 33.23 ml of the 12 th month of using the implant (P<0.05). Hemoglobin concentrations showed no changes, but serum ferritin concentrations were slightly increased. No changes in liver function, kidney function, glucose tolerance test and lipoprotein levels were found. Determinations of sex hormones (FSH, LH, E 2 and progesterone) levels, ultrasonography of ovary, and endometrial biopsy in observed group (n=9) showed that all had normal ovulation before insertion. But ovulation was suppressed and endometrium development was inhibited after insertion. All basal body temperatures were single phase patterns during the 1 year follow up. This study suggested that CaproF is an effective, safe and acceptable long acting contraceptive method. It is likely to reach its contraceptive effectiveness through suppressing ovulation, inhibiting endometrium development and influencing cervical mucus characteristics. CaproF is a biodegradable subcutaneous contraceptive implant of releasing levonorgestrel (LNG), which is expected to provide an effective contraception for 2 years. This study was undertaken to assess the one year preliminary clinical results of using CaproF in 19 subjects. All subjects (n = 19) completed the 1 year study, and the contraceptive effectiveness and follow up rate were both 100%. The incidence of side effects was low. The major side effects were menstrual disorder, but bleeding patterns tended to be improved and restored to be the same There was no significant increase in weight (P> 0.05) and no changes in blood pressure. In the 3 rd, 6 th and 12 th months after using CaproF, the cervical mucus became scanty and viscous without fern The amount of menstrual blood loss decreased from 49.38 ml of pre implantation to 33.23 ml of the 12 th month of the implant (P <0.05). Hemoglobin concentrations sho No changes in liver function, kidney function, glucose tolerance test and lipoprotein levels were found. Determinations of sex hormones (FSH, LH, E2 and progesterone) levels, ultrasonography of ovary, But ovulation was suppressed and endometrial development was inhibited after insertion. All basal body temperatures were single phase patterns during the 1 year follow up. that CaproF is an effective, safe and acceptable long acting contraceptive method. It is likely to reach its contraceptive effectiveness through suppressing ovulation, inhibiting endometrium development and influencing cervical mucus characteristics.