Prediabetes increases oxidative stress and the risk of type 2 diabetes and related cardiovascular diseases. Previous trials have shown antioxidant-rich strawberries improve this risk, but effects on antioxidant markers are inconclusive. This 28-week randomized controlled crossover trial evaluated the effects of freeze-dried strawberries (FDS) on fasting glucose, serum antioxidant status, and vascular inflammation in adults with prediabetes not on glucose-lowering medications. Participants were assigned to FDS (32 g/day ~ 2.5 servings of whole strawberries) or control (usual diet, no strawberries) for 12 weeks each, separated by a 4-week washout (n = 25/treatment period). Biomarkers were measured at baseline, 12, 16 (baseline 2), and 28 weeks. A mixed-model analysis of variance detected differences between groups, adjusting for covariates. Compared to control, FDS significantly improved serum superoxide dismutase (0.08 ± 0.04 U/mL), glutathione [(GSH): 1.8 ± 0.96 µmol/L], antioxidant capacity [(AC): 5.9 ± 3.2 µmol/L], β-carotene (113.9 ± 15.8 nmol/L), fasting glucose (97 ± 12 mg/dL), intercellular adhesion molecule [(ICAM): 56.0 ± 21.8 ng/mL], and vascular cell adhesion molecule [(VCAM): 440 ± 163 ng/mL] (all p < 0.05). ICAM was inversely correlated with GSH (r = −0.21), AC (r = −0.15), and β-carotene (r = −0.13) (all p < 0.05). VCAM was inversely correlated with AC (r = −0.12) (p < 0.05). Catalase, glutathione reductase, glutathione peroxidase, α-carotene, P-selectin, and E-selectin were unaffected. Our findings support strawberry intake as a dietary intervention for improving blood glucose control and antioxidant status in adults with prediabetes.