The study aims to compare the effectiveness of Guided Inquiry Learning (GIL) and Problem-Based Learning (PBL) model. A number of prior studies have implemented the GIL model for a limited area such as science. Similar to the PBL learning design, the previous studies that highlighted the application of GIL model was commonly targeted to find out its comparison with the traditional learning models. There was no relevant study that specifically compared both models in the explanatory writing activity to discuss the human respiratory system and its disturbances. The current study applied a quasi-experimental design by involving the fifth-grade primary school students of the 2018/19 academic year in Surakarta as the population. Meanwhile, the sample consisted of 162 students that were selected through multi-stage sampling. The data consisted of the students' explanatory writing test scores that were analyzed through a one-way ANOVA. The findings confirm that the GIL model is considered more effective than PBL for the explanatory writing activity due to the students' concrete operational age that still requires teacher-centred guidance in producing explanatory texts. With regards to the condition, the PBL model cannot offer effectiveness for the explanatory writing activity, as the model mainly emphasizes the students' problem-solving skills.