The potential of Haematococcus pluvialis powder in alleviating urinary tract obstruction-induced renal fibrosis by ameliorating mitochondrial dysfunction and epithelial–mesenchymal transition (EMT) was investigated in this study. Various methods, including the CCK8 assay, immunofluorescence, mitochondrial membrane potential measurement, mitochondrial reactive oxygen species detection assay, and immunohistochemical staining, were used for validation. The results demonstrated the ability of H. pluvialis powder in mitigating renal pathological changes in rats induced by unilateral ureteral obstruction (UUO) surgery. Compared with the model group, treatment with H. pluvialis powder significantly decreased fibronectin 1 expression (65.52%). In vitro, H. pluvialis powder ameliorated transforming growth factor-β1-induced changes in EMT markers in HK-2 cells, with the positive area fraction of E-cadherin increasing by 51.35%, and those of N-cadherin and vimentin decreasing by 62.30% and 39.36%, respectively. An increase in mitochondrial membrane potential and a decrease in mitochondrial superoxide accumulation were also observed. Subsequently, astaxanthin (AST) was used to intervene in the rat UUO and HK-2 pro-fibrotic cell models. The results revealed that H. pluvialis powder outperformed AST at equivalent dosages/concentrations. In summary, this study found that H. pluvialis powder could alleviate the pathological progression of renal fibrosis caused by urinary tract obstruction via mechanisms that include improving extracellular matrix deposition, reducing renal cortical injury, modulating the EMT process, and mitigating mitochondrial dysfunction. Therefore, H. pluvialis powder shows potential for the development of functional foods with renoprotective effects.