The study aimed to examine the effectiveness of Java E-Activities through the Internet on developing some Reasoning Thinking skills in Geometry and achievement among Prep – Stage Students, The study sample consisted of (60) students from prep First grade Students in Umluj – Tabuk- Kingdom of Saudi Arabia Which was divided into an experimental group (30) Students and a control group (30) students , Was preparing a list of reasoning thinking skills included the three main skills And (18) skill subset, as they contain the skill to Deductive thinking skills (6) the skills of sub-skill to Inductive thinking skills to (6) Skills sub-skill of Thinking skills representative (6) sub-skills, and Prepared the Study Tools That Included (reasoning thinking test in mathematics, Achievement Test in Geometry), and Applied these Study Tools Previously on the Study Sample, Then the researchers taught the Measurement unit using the according to Java E-Activities through the Internet the teacher's guide to experimental group , After that, the application of the study tools on the group students, and Tabulating the data and analyzing them Statistically, the study found that: • Effectiveness of Java E-Activities through the Internet on developing some reasoning thinking skills among prep First grade Students. • Effectiveness of Java E-Activities through the Internet on developing achievement in geometry among prep First grade Students. • positive relationship and strong and statistically significant between reasoning thinking skills and achievement in geometry of prep First grade Students