Introduction: Placenta morphometry varies with increased heavy metal concentrations among other factors. There is limited knowledge on the effect of perceived heavy metal exposure due to mining activities on placenta morphometry specific to the Tanzanian population. The study thus aimed to determine the morphometric characteristics of the human placenta and the association between placental weight with maternal factors in mining and non-mining areas in Northwestern Tanzania. Subjects and Methods: This was a comparative cross-sectional study conducted in Mwanza and Geita regions of Northwestern Tanzania representing the mining and non-mining areas, respectively. Included in the study were placentas from 490 mothers, residing in the respective areas throughout pregnancy. Comparison of the placenta morphometric variables between the two groups was made using the independent sample t-test, and association between the maternal factors and placenta weight was done using multi-level linear analysis. Results: The mean placenta weight in the non-mining and mining areas was 465.9±101.2 g and 443.6±82.7g, and the mean thickness was 1.52±0.32cm and 1.61±0.38cm respectively. The mean diameter in the non-mining and mining areas was 19.0±1.9cm, the mean cotyledon number was 20±5 and 19±4, and the mean cord length was 49.0±12.7cm and 50.1 ±10.4cm respectively. With the exception of cord length, the differences in the morphometric parameters in the non-mining and mining areas were significant p<0.5.  Increase in maternal weight on booking and maternal age were associated with corresponding increase in placenta weight. Conclusion: The findings of this study seem to suggest that heavy metal exposure due to mining activities does affect placenta growth.