A novel system for monitoring methane emission from a flooded paddy field was developed in order to quantify the greenhouse gas emission in near‐natural conditions. A paddy field planted with rice was covered by a semi‐open vinyl tunnel (1.8 × 10 × 2.5 m), and the methane concentrations inside and outside the tunnel were measured continuously from the booting stage to the ripening stage (August–September) using a methane gas detector. Methane emission rates were calculated on an hourly basis from the differences between the internal and external methane concentrations and the natural diffusion rates determined using a tracer gas method. The results indicated that the paddy field emitted 0.41–1.32 g methane m−2 day−1 during the two growth stages. The vinyl tunnel had no adverse effect on the growth and yield of rice plants inside. Despite the disadvantage of non‐accurate estimation under windy conditions, the technique is considered to be of potential value for evaluating methane emissions from a flooded paddy field.

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