The number of leukocytes in the circulating blood of amphibians is related to their health status, and the ratio of neutrophils to lymphocytes (N/L ratio) can be considered as a surrogate indicator of their stress level. In this paper, we reviewed the common blood sampling positions, methods and precautions for blood sampling in amphibians, summarized the effects of multiple factors including species, developmental stage, urbanization, environmental pollutants, temperature and disease on the percentages of neutrophils and lymphocytes and the N/L ratio, and the relationship between the N/L ratio and stress response capacity in amphibians. Combined with amphibian’s life history characteristics, at least three further areas of work should be urgently carried out:1) Optimalization and standardization of blood sampling technique for the tadpoles, juvenile and adult amphibians, and making it suitable for amphibian research in the field; 2) It is optimal to clearly define the relationship between a single factor and the percentage of neutrophils, the percentage of lymphocytes, and their ratio in the blood of tadpoles, juvenile and adult amphibians; Meanwhile, it is also important to clarify the relationship between the health status of amphibian and these above-mentioned indicators in the short term or for a longer period under the combination of multiple factors; 3) From the immunological point of view, to clarify whether there is a trade-off relationship between different components of the immune system and between immune function and other energy-consuming physiological activities for some key life history stages from aquatic to terrestrial phase transitions, and to provide a novel idea for estimating the future fate of amphibian population. The percentage of neutrophils and lymphocytes, as well as their ratio in amphibian blood is affected by many factors, and current studies focus on intraspecific comparisons under the condition of a single factor. It is necessary to cooperate with other physiological indicators, and to interpret their ecological significances carefully if these indicators will be applied under the conditions of multiple factors or for interspecific comparative studies.