This paper reports a case study which involved 32 secondary school students participating in an online collaborative learning (OCL) activity known as Diary of Discovering Geometry. This activity aimed to explore the real contents in the learners' surrounding for discovering the spatial concepts and the applications of geometry. The purpose of the study was to explore and investigate the online interaction that occurred in Diary and the perceived effects of Diary. A combination of descriptive and qualitative approaches was utilized to analyze the data. Findings indicate that the students tended to follow rather than being pro-active in Diary online interaction. The gain of knowledge in geometry was minimal. However, a majority of the participants perceived Diary positively as to increase their interest in computer, geometry and to share knowledge among the participants. Their interest in Diary decreased according to time. This can be remedied by introducing some interesting activities in order to maintain their interest throughout the activity. Discussion on the possible reasons of affecting online interaction was discussed. Limitation and recommendation based on the findings were also presented.