Objective Interspike intervals (ISI) of neuron action potentials contain a store of spatiotemporal coding information, yet the physiologic information in the spatiotemporal coding information was not revealed well. In this research, the physiologic information was quantified and analyzed in the ISI series by sample entropy (SampEn) method. Methods Using extracellular multi-unit in vivo recording, response action potential for sinusoidal gratings stimulus in cat primary visual cortex was recorded in this paper. And the jitter method was proposed to create new ISI series that were equivalent to original ones in different time scales. Physiologic information in ISI series was analyzed based on SampEn. This paper analyzed the correlation between SampEn and firing rate, the relationship between SampEn and direction selectivity, and the change of the SampEn with time scales. Results SampEn of neurons was of significantly negative correlation with firing rate in the whole time scales, and was of remarkably negative correlation with direction selectivity on six of eight neurons. And the SampEn of neurons was of weakly negative correlation with time scales. Conclusions SampEn reflects physiologic information of neurons in a certain degree and provides a reference for the physiologic information research of ISI series in nervous system.