This research explores effects of lesson study on science teacher learning and classroom practice in three purposively selected middle schools of Eritrea. An extended teacher development program that combined training workshops with actual practising of lesson study contributed in enhancing conceptual understanding and pedagogical skills of teachers. The participants valued lesson study as worthwhile teacher development strategy because it brought teachers together and hence significantly contributed in minimising teacher isolation. The finding of this research provides new insights into teacher professional development in Eritrea concerning implementation of lesson study as professional development process for science teaching.