This study aimed to examine the effect of the problem-based learning (PBL) on science attitudes of middle school students from low socio-economic status families. For this purpose, two intact classes of the same teacher were randomly assigned as experimental and control groups. In the unit of genetics, the experimental group was taught by PBL while the control group received traditional instruction. Students' attitudes were measured in terms of adoption of scientific attitudes, enjoyment of science lessons, and career interest in science administering a self-report instrument as a pre-test and a post-test. Results showed that after the treatment, although there were not statistically significant differences between two groups with respect to attitude toward science; in the experimental group, the mean scores were found to be consistently higher across all attitude dimensions compared to the control group. In addition, the mean scores suggested an improvement in the attitudes of experimental group students from pre-test to post test. Qualitative findings also revealed that students found PBL enjoyable. According to PBL students, searching for information and writing reports were among the features of the PBL contributing to their learning the most.