Applying Weller’s allometric model for partial organs, the self-thinning exponent α_x in overcrowded Bruguiera gymnorrhiza stands were examined. The self-thinning exponent α_x (=1/{1-(δ_x+θ_x)}) was estimated to be 1.52, 1.51, 1.09 and 1.45 in stem, branch, leaf and aboveground, respectively. The ρ-w relationship, where population density ρ is a response variable and mass w is an explanatory variable gives the α_x calculated from 1/ϕ_x, which is mathematically and statistically (in terms of OLS) equivalent to 1/{1-(δ_x+θ_x)}. The ϕ_x-values of 0.6582, 0.6601, 0.9129 and 0.6748, which are the same as the reciprocal of 1.52, 1.51, 1.09 and 1.48 in stem, branch, leaf and aboveground, respectively. The ϕ_x-value was not significantly different from 2/3, but significantly different from 3/4 in stem, branch and aboveground. This means that the α_x of woody parts were not significantly different from 3/2. The ϕ_L-value of leaf was significantly different from 2/3 and 3/4, but was insignificantly different from 1.0. These means that the stand leaf biomass is constant regardless of ρ. Therefore, the present results based on the allometric model of partial organs in the overcrowded B. gymnorrhiza stands strengthened the justification of the simple geometric model rather than the metabolic model.