Introduction: Many factors can affect ablation outcome in patients with papillary thyroid cancer. One of the good predictors is stimulated Tg (sTg). Since it is influenced by many factors including serum TSH level, it was postulated that sTg /TSH can be a more accurate predictor. Aim to compare the role of sTg and sTg/TSH as predictors of ablation outcome post first dose of RAI131 therapy in patients with papillary thyroid cancer. Results: Data of 126 patients with papillary thyroid cancer presented post-operatively for 131I ablation were retrospectively analyzed. Preablative sTg, TSH and sTg/TSH ratio had a range of 2.9-59.8, 31.4-127.9 and 0.027-1.97 together with a median value of 7.41, 61.3 and 0.089 respectively. Follow up sTg and diagnostic WBS confirmed successful complete ablation in 94 patients (74.6 %) with partial ablation in the remaining 32 patients. The measured cutoff value for prediction of successful ablation outcome of sTg and sTg/TSH ratio was 8.25 and 0.105, with sensitivity of 77.6% and 72.3% and specificity of 47% and 75% respectively, with statistically significant difference in the latter in favor of sTg/TSH. Positive postoperative neck US, positive lymph node (LN) involvement , multifocality and lower 131I ablative dose together with sTg and sTg/TSH above reported cutoff values are significantly associated with ablation failure post first 131I dose.Conclusion: sTg level and sTg/ sTSH ratio with cutoff values of 8.25 and 0.105 respectively have comparable sensitivity (77.6% versus72.3%) in prediction of ablation outcome post first ablation dose of 131I with no statistically significant difference. Yet, the sTg/ sTSH ratio has significantly higher specificity (75% versus 47%), raising the additive value of sTg/TSH ratio in clinical practice for prediction of ablation outcome.