The tensile yield behaviour of an aliphatic polyketone is studied in relation to the molecular relaxation processes present in the polymer. Dynamic mechanical thermal analysis reveals the presence of three molecular relaxation mechanisms; the crystalline alpha-, and the amorphous beta- and, gamma-process. The tensile yield behaviour, measured over a large range of temperature and strain rate, also gives evidence of these three relaxation mechanisms. The increase of the water content from 0.5 to 2.3 wt% leads to a selective change in the beta-contribution, whereas the alpha- and gamma-processes show little to no change. With respect to the tensile yield behaviour this leads to a reduction of the yield stress at high strain rates and/or low temperatures.