In Chinese cabbage (Brassica rapa L. var. pekinensis), the hybrid progeny of selected parental inbred lines exhibits superiority in yield compared to their parents. This phenomenon is known as hybrid vigor or heterosis. F1 hybrid varieties have increased yield in Chinese cabbage and are now widely used in crops. However, the molecular mechanism of heterosis is still a mystery. In this study, we examined the distribution of trimethylation of lysine 4 of histone H3 (H3K4me3), H3K9me2, H3K27me3, and H3K36me3 marks in the commercial F1 variety of Chinese cabbage (‘W77’) and its parental lines by chromatin immunoprecipitation sequencing at the early developmental stage. There is heterosis in cotyledon size after several days after sowing and F1 plants showed larger leaf size. We identified genes that were differentially histone-modified (DHMGs) in all four histone marks. In the F1, most of the histone marks were additive, and only a small number of genes showed non-additive histone marks for all four histone marks, suggesting that the histone marks of parents were heritable to the F1. Over 80% of DHMGs between parental lines of all four histone marks showed a high‒parent (HP) pattern in the F1, suggesting that HP-like histone modifications in the F1 might be associated with the epigenetic regulation of heterosis at the early developmental stage of Chinese cabbage. QTL analysis using the F2 population derived from‘W77’ indicates that dominant effects may be important for heterosis. Therefore, histone modifications may be important for maintaining the parental state to exert a dominant effect.