Аннотация:All available photometry for the Cepheid KN Cen is analyzed to construct its $$(O-C)$$ diagram spanning a 134-year long time interval. This made it possible for the first time to compute the rate of evolutionary period increase of the Cepheid, $$dP/dt=+2.91(\pm{1.68})$$ s yr$${}^{-1}$$, which is consistent with the results of model computations for the third crossing of the instability strip. The test for stability of pulsations proposed by Lombard and Koen confirmed the reality of the evolutionary period change.
