Background: Nonalcoholic fatty liver disease (NAFLD) is a leading cause of liver damage, and it affects about 24% of the population worldwide. This study aimed to investigate the effect of omeprazole and Spirulina platensis on hepatic and serum biochemical alterations in NAFLD induced by high-fat diet (HFD). Methods: Male Wistar rats were divided into four groups; one served as a normal control. The other groups received HFD and subdivided into three subgroups; one was left untreated and the other two groups were treated orally with either omeprazole (10 mg/kg) or Spirulina (1000 mg/kg) for 30 consecutive days. Results: Omeprazole successfully decreased elevated serum pentraxin-3 (PTX-3) and cytokeratin-18 (CK-18) levels and hepatic sterol regulatory element binding protein-1c (SREBP-1c) expression, while Spirulina had better impact on decreasing liver function enzymes, lipid profile, and nuclear factor erythroid 2-related factor 2 (Nrf-2) levels compared to omeprazole. Both treatments had similar effects on normalizing glucose homeostasis, decreasing insulin resistance, and improving adipocytokine levels. Conclusion: Effects of omeprazole and Spirulina on markers of NAFLD appeared to be mediated by regulation of inflammatory, apoptotic, and oxidative mediators. Thus, omeprazole and Spirulina may find use as promising adjuvant therapy to ameliorate NAFLD. Research ethical committee of the faculty of pharmacy, Cairo University approved the research (BC 1479).