The characteristics of the flow-rate and pollution parameters of the domestic wastewater of a medium-size city (Sivas, Turkey) have been investigated. The design and the operating parameters of a wastewater treatment plant appropriate to such a settlement were also studied. Daily and monthly flow-rate measurements and wastewater samples were taken at the outlet. Peak values of the flow-rate were observed between the hours 09:00 and 14:00. Domestic wastewater production per capita was determined as 170.6 litres per day. The wastewater biological reaction ratio coefficient (k), the BOD5/COD ratio and the BOD5/N ratio varied in the ranges 0.113-0.312, 0.44-0.67 and 3.1-9.5 per day, respectively. Daily pollution load parameters per capita were determined as follows: 47.3 g for BOD5, 85.3 g for COD, 34.9 g for suspended solids, 7.9 g for nitrogen and 1.32 g for phosphorus.