Background: The lactational amenorrhea method (LAM) is modern contraceptives that rely on exclusive breastfeeding for six months without additional food or beverage. The mother is in a state of amenorrhea and delays arranging birth to a quality family.

Aim: The study aimed to determine the cause of the failure of LAM.

Method: Study design with the cross-sectional analytic survey, conducted on mothers who have babies 6-24 months of age as 79 respondents. The sampling technique using purposive sampling, data analysis chi-square, and logistic regression.

Result: This study showed parity (OR = 4.861; 95% CI = 0.991 - 23.852), education (OR = 0.525; 95% CI 0.073 - 3.758), work (OR = 2.087; 95% CI = 0.241 - 18.064), knowledge (OR = 20.481; 95% CI = 2.459 – 170.608), additional contraception other than LAM (OR = 2.894; 95% CI = 0.365 – 22.965), menstruation before six months (OR = 10.265; 95% CI = 1.283 – 82.150), breast pump ( OR = 1.843; 95% CI = 0.189 – 17.990) and socio-economic (OR = 9.843; 95% CI = 1.029 – 94.134).

Conclusion: In conclusion, all variables influenced LAM's failure, but the most influential was knowledge, menstruation before six months, and social-economic.

Keyword: LAM, breastfeeding, failure