We have purified cyclic AMP‐dependent protein kinase from the yeast Saccharomyces cerevisiae. The purified enzyme was inactive in the absence of cyclic AMP and displayed two protein bands on SDS gel electrophoresis. One was identified as the cAMP‐binding protein by chromatography on cAMP‐agarose. M r of the latter was 50 000 while the catalytic subunit had an M r of 59 000. The enzyme accepted yeast phosphorylase, glycogen synthase and fructose 1,6‐bisphosphatase as substrates. No inhibition by the mammalian protein kinase inhibitor was observed.