Pot culture experiment and laboratory experiments were carried out to study the feeding activity of brown plant hopper through honey dew test and certain biochemical constituents in the rice plant due to the application of fly ash. Among the various treatments, quantity of honey dew excreted in terms of area was significantly less in lignite fly ash (LFA) at 10 t ha-1 (9.6 mm²) followed by LFA 12.5 t ha^-1 (10 mm²) as against the maximum of 51.6 mm² in the untreated check. Honey dew excreted in the treatments bituminous fly ash (BFA) at 12.5 t ha^-1 and 10 t ha^-1 were 11.0 and 11.6 mm², respectively and these two treatments were on par with each other. The biochemical constituents of plants imposed with fly ash revealed that total phenol content, silicon and tannin content varied significantly among the treatments. Total phenol content was significantly high in LFA at 10 t ha-1 (6.03 mg g^-1) and LFA at 12.5 t ha^-1 (5.9 mg g^-1) followed by BFA 12.5 t ha^-1 (5.4 mg g^-1), against the minimum of untreated check (2.06 mg g-1). Silicon content was significantly high in LFA 10 t ha-1 (2.6 %) and BFA 12.5 t ha^-1 (2.5 %) as against the minimum of 1.0% in the untreated check. Tannin content was significantly high in LFA 7.5 t ha^-1 (9.1 mg g^-1) and 12.5 t ha^-1 (8.46 mg g^-1) as against the minimum of untreated check (2.43 mg g^-1). Similarly BFA and LFA at 1 t ha^-1 and 2.5 t ha^-1 were significantly on par with each other and their phenol, silicon and tannin content were comparatively lower than the high doses.