<i>Objectives:</i> The aim of this study was to screen lone atrial fibrillation (AF) patients for mutations in the genes <i>KCNJ2</i>, <i>KCNJ3 </i>and <i>KCNJ5</i>, all encoding potassium channels. Furthermore, we wanted to replicate the prior association of two single-nucleotide polymorphisms (SNPs) in <i>KCNJ5, </i>C171T (rs6590357) and G810T (rs7118824), with lone AF in Han Chinese. <i>Methods:</i> We sequenced the coding region and splice site of <i>KCNJ2</i>, <i>KCNJ3 </i>and <i>KCNJ5</i> in 187 early-onset lone-AF patients screening for mutations and counting SNP frequencies for the two noted SNPs in <i>KCNJ5</i>. <i>Results:</i> No mutations were found in <i>KCNJ2</i>, <i>KCNJ3</i> or <i>KCNJ5. </i>Both genotype distribution and allele frequencies of the SNPs rs6590357 and rs7118824 significantly differed between the AF and control group (p_genotype = 0.0067, p_allele = 0.0021 and p_genotype = 0.014, p_allele = 0.0101, respectively). On allele level, the OR for lone AF for rs6590357 was 1.77 (95% CI 1.16–2.73, p = 0.009) and for rs7118824 it was 1.71 (95% CI 1.13–2.57, p = 0.01) in a model adjusted for age and gender. <i>Conclusions:</i> Our findings indicate that rs6590357 and rs7118824 in <i>KCNJ5</i> are associated with early-onset lone AF in Caucasians. No mutations were found in the exon or splice site of <i>KCNJ2</i>, <i>KCNJ3</i> or <i>KCNJ5</i>.