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The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented. Two methods were used to characterize the crystallization rate: the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer, which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum, brass and stainless steel plates, respectively. As to the dominant influence factor, the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil. Instead, we propose the plate’s ability of removing the latent heat of crystallization from the specimen. Rheological measurement is sensitive to the crystallization process. The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.