The lethality of inorganic arsenic (As) and the threat it poses have made the development of efficient As detection systems a vital necessity. This research work demonstrates a sensing layer made of hydrous ferric oxide (Fe2H2O4) to detect As(III) and As(V) ions in a surface plasmon resonance system. The sensor conceptualizes on the strength of Fe2H2O4 to absorb As ions and the interaction of plasmon resonance towards the changes occurring on the sensing layer. Detection sensitivity values for As(III) and As(V) were 1.083 ℃ ppb–1 and 0.922 ℃ ppb–1, respectively, while the limit of detection for both ions was 0.6 ppb. These findings support the feasibility and potential of the sensor configuration towards paving future advancement in As detection systems.