Myxobolus stanlii sp. n. was described from largescale stonerollers (Campostoma oligolepis) from the Mobile River Basin in Alabama. The parasite was described using critical identifying morphological features, and the 18S small subunit ribosomal RNA (SSU rRNA) gene sequence. The spore body was ovoid, 10.03 ± 0.7 (7.5–11.0) μm long and 8.8 ± 1.5 (6.3–11.3) μm wide in frontal view. Spore thickness was 6.3 ± 2.7 (6.2–8.6) μm in sutural view. Polar capsules were pyriform, of equal size, and oriented in plane with the sutural ridge. Polar capsules were 2.45 ± 1.5 (range 2.1–4.3) μm in width and 4.6 ± 2.7 (range 4.5–6.9) μm in length. Based on the SSU rRNA gene sequence of Myxobolus stanlii sp. n. is most closely related to M. pseudodispar.