Abstract—Some physical and photochemical properties of a proteinxhlorophyll complex which can be extracted from spinach chloroplasts with dilute Triton X‐100, have been measured. The molar extinction coefficient at the red maximum (671mμ) is 6.8 × 104. Solutions of the complex are weakly fluorescent, having a quantum yield of about 0.01. The complex undergoes photoautooxidation in the presence of oxygen with a quantum yield of about 0.2 × 10‐‐4, and sensitizes the autooxidation ofp‐toluene‐diamine (quantum yield about 1×10‐‐3) and of ascorbic acid (quantum yield 0.25). The complex‐catalyzed reduction of ferricyanide, in the presence of a protein‐carotene complex, was confirmed; its quantum yield is about 8 × 10‐‐4. The protein‐chlorophyll complex does not undergo a Krasnovsky reaction, nor could sensitized reductions of dye by abscorbate be detected. When excess Triton is added to the protein‐chlorophyll complex, it is converted into a detergent colloid apparently identical to a previously described Tween colloid.The properties of the protein‐chlorophyll complex are compared with those of other state