Abstract: Provided herein are pharmaceutically acceptable formulations comprising wild type Complement Factor I (CFI) and variants thereof; in some embodiments the wild type CFI and variants thereof are part of a fusion construct, e.g. a fusion construct comprising human serum albumin. The formulations stabilize CFI against acute stresses during storage in either a liquid or lyophilized state. Also provided are methods of making the formulations, and methods of using the formulations in the treatment of diseases.