Halowax 1051 is the highest chlorinated technical chloronaphthalene mixture among seven known formulations of the Halowax series. Octa- and heptaCN homologue groups are the main CN constituents of Halowax 1051 with declared 90% and 10% contents, respectively. In this study, using an isotope dilution technique and HRGC/HRMS, octaCN and heptaCNs contents of six batches of Halowax 1051 were between 82-93% and 6.2- 17%, respectively. Also mono- to hexaCNs were found in Halowax 1051, and their content more or less varied according to the batch; also, the abundance of a particular CN congeners varied. Tetra-, penta- and hexaCNs have been found in all six batches of Halowax 1051 examined, and their contents varied between 0.0024-0.77%, 0.031-0.22%, and 0.21-0.82%, respectively. TriCNs have been found in three of six batches, and mono- and diCNs in two of six batches with 0.0020-0.40, 0.0017-0.25 and 0.0012-0.34% for positive findings, respectively. 2,3-DiCN (no. 10), 1,8-diCN (no. 9) at <0.0002 mg/g, 1,6,7-/2,3,6- triCNs (nos. 25/26), 1,3,8-triCN (no. 22) at <0.0002 mg/g, 1,3,6,7-tetra (no. 44), 1,2,3,6- tetra- (no. 29), 1,2,7,8-tetraCN (no. 41) and 1,2,3,6,7,9-hexaCN (no. 70) at <0.0005 mg/g have not been found in Halowax 1051.