Background: Preterm labor is still a global problem in some countries include Indonesia. In 2010, the preterm infant was 675,744 (4.5%) from globally population. It cause Indonesia was rank fifth in 10 countries in the world. Neonatal mortality is still high in preterm birth complications and 35% of the 3.1 million deaths in the world per year. Many surviving premature babies have experience in impairment of cognitive, vision, and hearing. The purpose of this study was to know the risk factors of pregnant women most related with preterm labor at the Hospital PKU 1 Muhammadiyah Yogyakarta. Methods: This study was an observational analytic study with cross sectional design. The sample of this study was maternal medical record at the Hospital PKU 1 Muhammadiyah Yogyakarta in April 2014 until September 2017 with inclusion and exclusion criteria. Data analysis used chi-square test and logistic regression. Results: The bivariate analysis shows that there are no relation between infection (p=0.268, OR=1.51; 95% CI 0.727-3.123) and premature rupture of membranes (PROM) (p=0.380; OR=1.36; 95% CI 0.683-2.719) with preterm labor. There are relations between previous premature history (p=0.001; OR=2, 17; 95% CI 1.800- 2.609) and age (p=0,01; OR= 3,24; 95% CI 1,589-6,604) with preterm labor. Conclusion: There are no relations between infection and premature rupture of membranes (PROM) with preterm labor. There are relations between previous premature history and age with preterm labor. The most influential factor in preterm labor is age.