This study aimed at investigating effectiveness of an e-training environment management strategy in developing blended learning design competencies of secondary stage female teachers in the kingdom of Bahrain. The developmental research methodology was used. Blended learning activities’ design competencies needed by secondary stage female teachers were derived. An e-training environment management strategy was developed. Furthermore, a list of instructional design standards was derived. The researcher then developed an e-training environment based on a strategy for activity management in accordance with Elgazzar (2014) instructional design model. Research tools constructed by the researcher included: An achievement test for the cognitive skills, a product assessment card for the performance skills of blended learning design competencies, and a performance observation card for interaction with elements of the e-training environment. Validity and reliability of the research tools were ascertained. A sample of 42 secondary stage female teachers were selected and divided into two equal experimental and control groups of 21 teachers. The experimental group was trained using activity management strategy in an e-training environment, whereas, the control group did not receive any training. Research experiment was conducted with pre and post applications of research tools. Results of the study revealed statistically significant differences in the post application between experimental and control groups with respect to cognitive skills achievement test of blended learning design competencies, and such differences were in favor of the experimental group. Such statistically significant differences were in favor of the experimental group with respect to the product assessment card and the performance observation card. Based on results of the study some relevant recommendations were made.