Objective: To determine the impact of seasonal variations on health indices of free-ranging asymptomatic guinea fowls (Numida meleagris) in Zambia. Methods: A time series analysis was carried out on a prospective cohort study over a 12 month period between March 2010 and February 2011 by examining a total 147 guinea fowls for haematological and morphometric data of selected organs. Results: There was a strong correlation in erythrocytic indices between packed cell volume and red blood cell counts (=0.824, P<0.001) as well as between packed cell volume and hemoglobulin (Hb) counts (r=0.648, P<0.001). Seasonal differences showed that erythrocytic indices were higher in the males than the females and that the difference was significantly higher (P<0.001) during the rainy season, which coincided with the breeding period when females were laying eggs. Increase in total plasma protein was positively correlated with overall body weight. Generally, females had higher body weights and total plasma protein levels than the males in the rain season. Of the 147 birds examined, 51% (n=147) had the bursa of Fabricius. For birds that had the bursa of Fabricius, the weights of bursae were higher (P<0.05) in the cold-dry season than the other seasons and no sex differences were observed. Spleen morphometric data did not show any seasonal nor sex differences. Conclusions: Overall, data presented herein demonstrate that seasonal variations have a significant influence on health indices of free-ranging guinea fowls and that these factors could influence the susceptibility of this species of birds to disease infections at different times of the year.