When laboratory accidents in schools, especially in recent years, are examined, it is remarkable that many of these events resulted from the incorrect implementation of laboratory safety. The most significant role in the administration of laboratory safety belongs to science teachers. During this process, the necessity of laboratory safety training is for teachers to gain knowledge, skills, and attitude with regard to laboratory safety. This study aimed to investigate science teachers' knowledge level regarding laboratory safety and increase science teachers' knowledge level regarding laboratory safety through professional development seminars. Professional development seminars were carried out for teachers in eight modules which included both visual presentations and active learning-teaching activities. Training activities were planned in consideration of the subjects and experiments included in the current Turkish general science curriculum. The single-group pre-test post-test design, a semi-experimental design application, was used. To investigate the effects of laboratory safety professional development seminars, pre- and post-tests were applied to only one group. The "Laboratory Safety Knowledge Test" developed by the researchers was applied to determine teachers' improvement regarding laboratory safety. According to findings, there was a statistically significant difference between scores of changes in teachers' knowledge level regarding laboratory safety before and after professional seminars. Moreover, there was not a demographically significant difference between scores of changes in teachers' knowledge level. It is considered that the findings of the research will contribute to school laboratories being safer and more effective environments in which the activities of science lessons are carried out.