The levels of serum retinol, total serum proteins, serum albumin, serum globulins, albumin/globulin ratio, haemoglobin concentration, haematocrit, body weights as well as dynamics of A. galli (namely eggs per gram of faeces, worm establishment rate, total counts, male and female counts, females to males ratio, total worms weight and fecundity) were investigated in chickens experimentally infected with 350 eggs of A. galli and daily supplemented with 1500 I.U retinyl acetate. Forty, ISA brown chickens aged eight weeks were divided into four equal groups. The effect of infection alone was investigated in the infected chickens in group I. The effects of infection and supplementation were investigated in chickens in group II. Chickens in group III were neither infected nor supplemented. The effect of supplementation alone was investigated in chickens in group IV. The dynamics of A. galli was investigated in supplemented and non-supplemented chickens. Mean levels of retinol, albumin, albumin/globulin ratio, haematological parameters and body weights were significantly (p<0.05) low in the infected than in non-infected groups. A. galli infection had significant effect on globulin levels when birds were supplemented (p<0.05). The above mentioned parameters were significantly higher in the supplemented than in the non-supplemented groups (p<0.05). Mean EPG, fecundity, female: male ratio and female worms counts were significantly (p<0.05) higher in the non-supplemented than in the supplemented groups. Vitamin A supplementation did not significantly (P>0.05) affect total worm counts, male worms counts, establishment and total worms weights. It is concluded that A. galli infestation lowers serum retinol, total proteins, albumin, albumin/globulin ratio as well as haemoglobin concentrations, haematocrit and body weight, and that, vitamin A supplementation improves the levels of the above mentioned parameters and lowers egg counts and fecundity and favours development of male worms. Supplementation of commercial feeds with stabilized vitamin A is highly recommended.Ministry of Education and Vocational Training, Tanzania