Lack of data especially pertaining to the chemistry of mangrove wood species makes it difficult to prepare successful plans for their conservation and to use mangroves as a source of wood fiber. In this paper, chemical characterizations of the six main mangrove species of Bangladesh [namely Keora (Sonneratia apetala), Geoa (Excoecaria agallocha), Bine (Avicennia alba), Sundari (Heritiera fomes) Pashur (Xyloccarpous mekongests), and Kakra (Bruguiera gymnorhiza)] were investigated. The chemical results revealed that these species contain high percentages of dichloromethane followed by methanol extractives. Methanol extracts in Pashur, Sundari, and Bine were higher than 10%, which indicates high percentage of tannin material. The total lignin content in these species was higher than 25%, except for Gewa (23.6%) and Pashur (21.3%), which is higher than that of the normal range of hardwood. The pentosan content in these six species was within the range of 19.4–22.8%. The a-cellulose content in Keora and Gewa was acceptable for pulp production, but the others were lower than the normal range of hardwood. Alkaline nitrobenzene oxidation showed that all these species had a very high syringaldehyde to vanillin (2.6–5.0) ratio except Keora (1.6). Surprisingly, rhamnose is the main constituent with xylose of hemicelluloses of these six mangrove species. The ash content in these six mangrove wood species was also higher than that in normal hardwood.