Design variables of e-learning technologies have gained great attention and concern from developers as well as researchers. So, e-Games design has gained a special concern in its design as an e- Learning technology in accordance with learning theories and instructional models such as Gagne’s theory. This research aims at investigating the effectiveness of an instructional e-game program designed according to the Gagne’s theory on developing mathematics’ achievement among primary school pupils in Saudi Arabia. The research sample composed of 46 female pupils from the fifth grade pupils at King Fahd University of Petroleum and Minerals’ primary schools. Thus, the Developmental Research Method was adopted. The study sample was selected as a purposed cluster one of two classes (sections). The quasi-experimental design with pre and post testing was used. The sample was divided to two equal groups which were randomly assigned as: experimental group 1 (e-Games with Gagne’s theory), experimental group 2 (e-Games without Gagne’s theory); (23) female pupils in each group. An instructional unit has been selected from the 5th grade mathematics curriculum, its content was analyzed to drive the mathematical achievement categories of knowledge and cognitive skills. Then, a list of instructional design standards was derived for designing the instructional e-Games. The two instructional e-games programs were developed by the 1st author using Elgazzar (2002) ISD Model of the 2nd author: one e-Games program with Gagne’s theory and the other one e-Games program without Gagne’s theory. Both the instructional e-games programs were refereed, revised and approved according to those derived standards of instructional design. A Mathematics Achievement Test was developed and approved to be valid and reliable. The 1st author carried out the research experiment according to the experimental design. So; the first experimental group 1 was taught using the e-Games program (according to Ga- gne’s theory), and the experimental group 2 was taught using e-Games program (without Gagne’s theory). The research instrument was implemented pre and post experimentation according to the experimental design. Data were collected and encoded to the SPSS package and ana-lyzed using appropriate statistical methods to test the research hypotheses. Research results have revealed that there is no effectiveness of e-Games Program with Gagne’s theory as compared with e-Games without Gagne’ Theory in developing the Achievement of Mathematics, and this result gives an answer to the main research question that designing instructional e-Games program based on Gagne’s Theory doesn’t have any comparative Effectiveness in Developing Saudi female pupils’ in the Achievement of Mathematics. This result calls for further research on other learning outcomes of Mathematics’ learning. The article includes Tables, References, Recommendations, and a list of proposed future researches.