Estimation of the population size of oriental weather loach (Misgurnus anguillicaudatus) was attempted using the removal method and the mark-and-recapture method in paddy plots in Kaminokawa City, Kawachi County, Tochigi Prefecture in 2007 and 2008. Removal surveys were conducted four times in each of the three study sites (950 m2, 950 m2 and 1,000 m2 in area) established in two paddy plots from 15 June to 6 August, 2007. The mark-and-recapture surveys were done twice in each of two sites (1,900 m2 and 1,000 m2) established in the two paddy plots from 15 June to 3 August, 2008. The estimated population size (population density; individuals per 1 m2) excluding unreliable estimation values, by the two methods ranged from 538 (0.54) to 1,526 (1.61). Based on these results, several proposals on the estimation method of the loach in paddy fields are given.