Hygrophila spinosa T. Anders plant seeds (HST) possessing gelling behavior with mineral constituents have been chosen as a dopant in cobalt oxide (Co 3O4) to investigate the humidity sensing properties. The study on the structural parameters, functional groups, BET surface area, surface morphology and elemental analysis of the prepared sensor samples was made using XRD, FT-IR, nitrogen adsorption/desorption isotherms at 77 K, SEM and EDX techniques respectively. The humidity sensitivity factor (Sf) of the prepared samples was evaluated by two probe dc-electrical resistance method at different humidity levels. The Sf value determined suggested that the sample with the weight ratio of Co3O4:HST biominerals of 0.25:0.75 respectively was beneficial for increasing the sensitivity factor possessed relatively a higher value, i.e. 4500. Good linearity, reproducibility, stability and fast response time (5.5 ± 0.25 min) and recovery time (2.5 ± 0.08 min) achieved in CH3 sample is indicative to be a good humidity sensor. © 2012 Elsevier B.V. All rights reserved.