Objective The eighth version of the American Joint Committee on Cancer (8th AJCC) system for anaplastic thyroid carcinoma (ATC) added lymph node (LN) metastasis as the staging element. This study aimed to explore the association between LN status and ATC's prognosis, identify the optimal LN index and establish a novel prognostic model. Design and Patients Data of 199 ATC patients after surgery were collected from the Surveillance, Epidemiology and End Results (SEER) database, then randomly divided into training and validation cohorts. Measurements We compared the prognostic value of AJCC N status, number of positive LN (PLNN), ratio of LN (LNR) and log odds of positive LN (LODDS). We conducted univariate and multivariate Cox analyses to determine the independent prognostic factors for ATC, and constructed a novel prognostic model. The concordance index (C-index), area under the receiver-operating characteristic curve (AUC), calibration curves and decision curve analysis (DCA) were used to assess the nomogram's predictive performance. Results LODDS showed the highest accuracy among four LN systems to predict overall survival (OS) for ATC. In the training cohort, the C-index of the LODDS-based nomogram was 0.738. The AUCs were 0.813, 0.850 and 0.869 for predicting 1-, 2- and 3-year OS, respectively. The calibration plots and DCA indicated the great clinical applicability of the model. The above results were verified in the validation cohort. Conclusions LODDS showed better predictive performance than other LN schemes in ATC. The LODDS-incorporated nomogram has the potential to more precisely predict the prognosis for ATC patients than the AJCC system.