In order to observe the neurotrophin’s influence on intracellular free calcium concentration, the test neuron was labeled by fluorescence indicator Fluo-3, and imaged by self-built real-time fluorescence microscopy system. The authors observed the changes in intracellular free calcium concentration (［Ca2+］i) in the bovine retinal neurons under the influence of four kinds of neurotrophins such as brain derived neurotrophic factor BDNF. On account of the fact that fluorescence indicator’s intensity decays over time, it is necessary to apply a “decay removal correction” to the fluorescence intensity in order to show the fluorescence intensity that solely represents ［Ca2+］i. The corrected data shows an increase after adding neurotrophins to neurons, which is consistent with similar results published by other groups. Thus, our method of imaging living cells is feasible, and “decay removal correction” is reliable.