Abstract Background Serratus plane block is a thoracic truncal block that has been proposed as alternatives for analgesia such as epidural anesthesia and paravertebral block for the anterolateral chest wall. Previously, we performed the clinical study about optimal volume of the local anesthetic in serratus plane block. The primary aim of this study was to assess the pattern of distribution of dye into the serratus plane of cadavers after ultrasound-guided serratus plane injection. Findings Ultrasound-guided serratus plane injection was performed at the level of the fourth rib on the mid-axillary line in nine adult Thiel-embalmed cadavers. In each cadaver, one side was injected with 20 ml of methylene blue dye and the contralateral side with 40 ml. Dissections of the thoracic walls were performed 20 min after the injection. The spread of the dye to intercostal nerves, lateral and medial pectoral nerves, long thoracic nerve, and thoracodorsal nerves was assessed. All T2–T5 intercostal nerves in the 40-ml group and all T3–T4 nerves in the 20-ml group were stained with the dye. A larger number of intercostal nerves was stained in the 40-ml group than that in the 20-ml group. Medial and lateral pectoral nerves were not frequently stained in either group. Conclusions The range of craniocaudal spread of the injectate was wider in the 40-ml group than that in the 20-ml group after ultrasound-guided serratus plane injection in Thiel-embalmed cadavers.