Resumo. The aim of this study was to evaluate whether the density of occurrence of andirobeiras is dependent of the Amazon River distance, analyzing their spatial distribution and diameter structure of the population in a floodplain forest in Amapá state, Brazilian Amazon. This work is part of ‘Florestam’ project (ecology and forest management for the multiple use of the floodplains of the Amazon estuary).This study was conducted in an environment protected area of 136.59 ha, located in Fazendinha district, city of Macapá,AP state (00º03’04, 24 “S and 51º 07’42, 72” W). Three transects perpendicular to the Amazon river were launched, apart from each other every 500 m, to guide the direction and location of trees. All andirobeiras with (CBH) circumference at breast height ≥ 15 cm were inventoried and mapped. The number of diameter classes was defined according to Higushi. We tested the fit of andirobeira diameter distribution to the exponential model by Meyer. We calculated the ratio q of De Liocourt for the observed and for the estimated frequencies. We calculated Morisita index, variance/mean ratio, and aggregation to infer the spatial distribution. Six hundred and eighty productive and unproductive andirobeiras were inventoried with a basal area of 55.84 m2, generating a density of 5 trees ha-1.The diameter distribution were generated with 9 classes of 11 cm diameter range and the determination coefficient for the exponential model was 0.93 and the quotient q = 2.03.The indices used showed that the spatial distribution of adult andirobeiras occurs in the aggregate form. The andirobeira diameter structure shows great number of young individuals and that the population is not senescent. The density of adult andirobeiras depends on the river distance, with the greatest concentration of trees in more remote areas of Amazon River.