Ferredoxin‐NADP+ reductase (FNR, EC I.18.1.2) from the green algae Chlorella fusca Shihira et Kraus 211–15, was purified to homogeneity. The molecular mass was 36.8 kDa as determined by SDS‐polyacrylamide gel electrophoresis. The enzyme exhibits the typical spectrum of a flavoprotein with an absorption maximum at 459 nm and an A273/459 ratio of 7.2. It contains one mol of FAD per mol of protein and the calculated extinction coefficient is 9.8 mM cm−1. Four different forms of the purified enzyme were detected by isoelectric focusing (pI between 5.4 and 5.9), even when protease inhibitors were used during the first steps of the purification. Kinetic parameters were determined for several FNR‐catalyzed reactions. NADP+ photoreduction gave comparable rates when either ferredoxin or flavodoxin was used.