Malayan Sword or Borneo Sword (Aglaonema simplex) is a semi-aquatic plant that inhabits the swamp forest or adjacent to a river. The plant species belong to the Araceae family and are native to Southeast Asia. Ammonium is one source of nitrogen for plants. In higher concentrations, ammonium is toxic to plants. The present study examines the effects of ammonium concentrations (0 mM to 45.0 mM) on biomass, α-tocopherol, ascorbic acid, chlorophyll, carotenoid, phenolic, flavonoid, and flavones levels in an aquatic plant culture, Aglaonema simplex. Results showed that ammonium concentrations induced changes in the biomass and biochemicals of the plant. Ammonium at 36.0 mM produced the highest biomass at 1.5-fold dry weight, ascorbic acid at 1.2-fold and total phenolic produced 1.3-fold dry weight in biomass after 28 days of treatment. Carotenoid, chlorophyll, and flavonoid content varied among the ammonium concentrations and depend on the culture period. Ammonium concentrations did not significantly influence (p > 0.05) the α-tocopherol content in the treated plants. The finding suggested that ascorbic acid and phenolic might act as shields to diminish the effects of ammonium toxicity and can be induced by an appropriate ammonium concentration applied into the culture medium.