In this study, 24 experienced in-service teachers' science process skills (SPSs) development and their use of SPSs in their lesson plan through a week-long professional development (PD) supported by the Scientific and Technological Research Council of Turkey (#117B302) were studied. SPSs are important part of scientists' work, scientific literacy, science education, and problem solving. In this research, SPSs were examined under two main categories, (i) basic SPSs and (ii) integrated SPSs. Basic SPSs are prerequisite for development of integrated ones that have also two sub-categories, namely, verification type and authentic experiment design. Through the PD provided by chemistry teacher educators, participant chemistry teachers received a training that balanced both theory and application of inquiry strategy. In the PD, teachers participated in all activities sand conducted all activities that are chemistry experiments based on inquiry. Moreover, during the activities they wrote hypothesis, designed experiments, controlled variables, collected and analyzed the data, and presented their conclusions to other groups. The data were collected through a with 36 multiple choice items. The test was administered as preand post-test. The statistical analysis of the data was performed with SPSS.23 package program. To compare and contrast the scores, paired sample t-test was run. Results revealed that there is a statistically significant difference in teachers' SPSs score in favor of post-test (t=2.508, p <0.05). In the light of the results, it can be suggested that longitudinal PDs should be organized more frequently. Moreover, active participation of teachers into the activities should be provided.