Transgenic plant systems have successfully been used to express recombinant proteins, including rice seed-expressed recombinant human serum albumin (rHSA), without the risk of contamination of human pathogens. Developing an efficient extraction process is critical as the step determines recombinant protein concentration and purity, quantity of impurities, and process volume. This article evaluates the effect of pH and time on the extraction and stability of rHSA. The amount of rHSA in clarified extract after 60 min of solubilization increased with pH from 0.9 mg/g (pH 3.5) to 9.6 mg/g (pH 6.0), but not over time as 10 min was sufficient for solubilization. Total soluble protein in extracts also increased with pH from 3.9 mg/g (pH 3.5) to 19.7 mg/g (pH 6.0) in clarified extract. Extraction conditions that maximized rHSA purity were not optimal for rHSA stability and yield. Extraction at pH 3.5 resulted in high purity (78%), however, rHSA degraded over time. Similar purities (78%) were observed in pH 4.0 extracts yet rHSA remained stable. rHSA degradation was not observed in pH 4.5 and 6.0 extracts but higher native protein concentrations decreased purity. Strategies such as pH and temperature adjustment were effective for reducing rHSA degradation in pH 3.5 rice extracts. Low temperature pH 3.5 extraction retained high purity (97%) and rHSA stability. While seed-expressed recombinant proteins are known to be stable for up to 3 years, the degradation of rHSA was notably extensive (56% within 60 min) when extracted at low pH. (c) 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:681-691, 2018