Aims: Preterm birth is an important unresolved issue that affected from biological, social, environmental stress and genetic factors. According to its importance, present study was conducted to identify of modifiable risk factor of preterm birth in Gonabad City, Iran. Materials & Methods: This case-control study was performed on 73 preterm and 160 term infants in 22th of Bahman Hospital of Gonabad City, Iran, in 2014. Sampling of case group was convenience and control group was random. Data were collected by a researcher-made questionnaire from medical files and interviewing by mothers and then were analyzed by SPSS 18 and Chi-square, independent T, Exact Fisher, Kendall tau and logistic regression tests. Findings: Two groups were significantly different according to income levels, a history of premature birth, kind of delivery, occupation of father, location of residence, contribution in pregnancy classes (p<0.000), location of residence (p<0.001), number of children (p=0.046), unwanted pregnancy (p=0.005), mother's education level (p=0.042) and immigration status (p=0.012). A history of premature birth (OR=2.45; p=0.014), contribution in pregnancy classes (OR=2.81; p=0.007), income level (OR=0.068; p=0.002) and location of residence (OR=0.068; p=0.002) were predictors of preterm birth. Conclusion: A history of premature birth, contribution in pregnancy classes, income level and the location of residence were associated with chance of preterm birth.