This research belongs to a qualitative research employing descriptive comparative method. It purposes to explore and compare the register, genre and ideology of opinion text and editorial text issued in the Jakarta Post by using Systemic Functional Linguistics Approach. This is aimed to find out the similarities and differences of all texts. The research applies total sampling technique for all aspects of lexicogrammar approach, cohesion, text structure and genre which was considered as data. The source of data is the opinion text taken from the Jakarta Post newspaper on February, 3rd 2006, and the editorial text in www.thejakartapost.com on February, 8th 2006. The research is conducted by analyzing the data through the description of lexicogrammar, cohesion, text structure and genre to define the aspects of register, genre and ideology. Then, the research is purposed to discover the similarities and differences of all texts. Based on the data analysis, the interpretation of register between text I and text II involving field, tenor and mode can be concluded as follows. The interpretation of field describes that both texts have similar issue relating to Hamas’ victory. In sense of tenor, both of texts employ mostly same features. The degree of relationship between the writer and readers of text I and text II is equal and the status between the writer and the participants inside of both texts is unequal. The interpretation of affect shows that the text I uses negative judgment to the issue, but the text II judges positively to the issue. The contact illustrates that the readers both the texts are uninvolved. Even, both of the texts categorized as the solid language, but it is still high readability. The interpretation of mode signs that the language style of both texts tends to be spoken-written in which appropriates to the medium, either the Jakarta Post in newspaper, or internet media. The text I uses Discussion genre since the GSP consists of thesis – preview – arguments for – arguments against – conclusion and recommendation. The text describes that Hamas victory is considered as an opportunity to make the peaceful condition in the Middle East, especially for the Hamas from Palestine and Israel. Mean while, text II employs Exposition genre since its GSP compresses of thesis– preview – argument I – Argument II – Elaboration of the argument – Argument III – reiteration. The text illuminates that the other sides, such the U.S. Israel, and the U.N should give Hamas a chance to lead Palestine government. The ideology of editorial texts can be traced back through the interpretation of register including field, tenor, mode, and genre. The text I employs left protagonist ideology. Left means that the writer worried about the victory of Hamas issue. Therefore, the writer’s ideology tries to reject the victory of Hamas by implying his protagonist perspective. However, the text II employs right antagonist ideology. Right in this sense means that the writer has the power to gain. The positive judgment directed to the victory of Hamas in Palestine, in this case the writer positively supports its victory.