Objectives: The aim of this in vitro study was to evaluate the effects of citric acid containing fluoride, nano-hydroxyapatite, and casein on eroded enamel. Design: The crowns of 120 extracted bovine incisors were embedded in acrylic resin. An enamel window (2 × 3 mm) was created on the surface. Before in vitro pellicle formation samples were eroded in 1% citric acid (pH = 3.2) for 1 h at 36 °C and were randomly classified to eight groups (n = 15) as follows: Positive control: 1% citric acid, Negative control: Distilled water, F1: 0.047 mmol/L sodium fluoride, F2: 0.071 mmol/L sodium fluoride, NHA1: %0.05 Nano-Hydroxyapatite, NHA2: %0.1 Nano-Hydroxyapatite, C1: %0.02 Casein, C2: %0.2 Casein. Erosion cycling was performed three times daily for 3 days. In each cycle, the samples were immersed in 10 mL of control or modified solutions (10 min) and in 10 mL of artificial saliva (60 min). The surface roughness and enamel loss were analyzed by using profilometer, scanning electron microscopy (SEM) and atomic force microscopy techniques (AFM). Results: Among the groups, the positive control group was found to be having the highest erosive wear. Erosive wear in the F2, NHA2, C1, and C2 groups was not significantly different from the negative control group (p > 0.05). The C1 and C2 groups showed that erosion terminated and minimal tissue recovery occurred on the enamel surface. Conclusion: Although all modifications reduced further demineralization, the citric acid modification with casein was found to be having a greater impact on dental erosion than the others.