This paper explains the result of the research conducted in order to find out: (1) whether there is a significant difference in writing achievement between the students taught using Task-Based Instruction and Group Investigation method; and (2) which method has a better result in writing, the group taught using Task-Based Instruction or using Group Investigation method. The method used within this research is quasi-experimental design. This research was led at SMA BATIK 2 Surakarta in the academic year of 2018/2019. The population of this research is the eleventh grade of SMA BATIK 2 Surakarta. The samples of this research are the XI IPA 3 as the experimental class which consists of 28 students and XI IPA 1 as the control class which consist of 28 students. The data within this experiment were gathered by the usage of mechanism to collects it. The data were analyzed using t-test formula. The calculation of the t-test data shows that t observation (to) = 2.02 is higher than t table (54, 0.05) = 1.960. Thus it can be concluded that there is a significant difference in writing achievement between the students taught using Task-Based Instruction and those taught using the Group Investigation method. The average score of the students taught using the Group Investigation is 77.64. Meanwhile, the average score of the student taught using Task-Based Instruction is 75.80. Therefore, it can be concluded that Group Investigation method has a better result in writing than Task-Based Instruction method.