Gender differences in reading are a common finding in international assessments with girls usually outperforming boys. The difference in reading between girls and boys has been highlighted as an educational challenge in most OECD countries, and the gap was significant for the Nordic countries. The Progress in International Reading Literacy Survey (PIRLS) is among the widely known international large assessment that focus solely in assessing reading achievement of 4th grade students. It offers the possibility to investigate how variability in various background context relate to reading achievement. Using PIRLS 2016, this study aims to investigate gender differences in reading achievement by accounting the contribution of different variables related to engagement in reading lessons, reading motivation, reading self-efficacy, sense of belonging at school, home characteristics (parents reading attitude, early literacy activities, early literacy tasks. The data is analysed using multiple regression analysis, and the gap in reading score would be decomposed for each Nordic country. The decomposition results suggest the reading score of boys increased if they have the same characteristics as girls. Reading motivation and early literacy skills before primary school account the most in explaining gender differences in reading achievements, while some of the gap remained unexplained.