The phenolics concentrations of rapeseed are important because they are antinutritional com-pound or directly positive related to antioxidant actives. In this study, single nucleotide poly-morphisms (SNPs) identified from genotyping-by-sequencing (GBS), and genome-wide associa-tion study of phenolic contents were investigated in 95 rapeseed mutant lines derived from gamma rays and their original cultivar. A total of 3,196,318 SNPs were detected, identifying a set of 70,208 union SNPs used to perform association studies. Six phenolics and glucosinolate (pro-goitrin) were identified, sinapine was the major phenolic compound (91.2–99.2%) in all geno-types. The association study was conducted for six phenolic compounds, progoitrin, total sinap-ine content (TSC), total phenolic content (TPC) and seed yield. The association study identified 241 SNPs that were significantly associated with six phenolic compounds, progoitrin, TSC and TPC. Based on the detected SNP markers, BnaA06g31740D, a gene associated progoitrin, BnaC-nng39930D, a gene associated trans-sinapine 1, BnaA07g31720D, a gene associated trans-sinapine 2, BnaC03g31950D and BnaA06g09180D, a gene associated TSC, and BnaAnng27700D, a gene associ-ated TPC, were selected as candidate genes. The SNP makers associated major phenolic com-pounds identified and could be used as targets for breeding programs aimed at improving anti-oxidant contents and reducing antinutritional components.