The self-thinning exponent α between mean aboveground mass w and population density in Bruguiera gymnorrhiza stands was found to be 1.469, which was not significantly different from 3/2. This results means that the 3/2 power law of self-thinning holds in the stands. The multiplying factor K was 12.40 kg m^-2α. Using Weller’s allometric model, the values of the allometric constant θ and the multiplying factor g_θ between mean tree height H and w were respectively estimated to be 0.2605 and 2.868 m kg^–θ, showing that H increased with increasing w. Simultaneously, the allometric constant δ and the multiplying factor g_δ between mean mass density d and w were respectively estimated to be 0.05894, which was not significantly different from zero, and 1.934 m^–3kg^1-δ, showing that d remains constant regardless of an increase of w. The α based on θ and δ, and K based on g_θ and g_δ were respectively estimated to be 1.469 and 12.4 kg m^-2α, which confirms that the 3/2 power law of self-thinning is undergoing in this stands. Therefore, the results based on the allometric model strengthen the justification of the simple geometric model proposed by Yoda et al. (1963). As far as the present overcrowded B. gymnorrhiza stands are concerned, the self-thinning can be explained by the simple geometric model.