This study was conducted to assess the humoral immune response to Peste des petits ruminants (PPR) vaccination in West African Dwarf (WAD) sheep experimentally infected with Trypanosoma congolense (Tc). Twenty adult WAD sheep, assigned to five groups of four sheep each were used. Group A sheep were neither vaccinated nor infected, while all sheep in groups B-E were vaccinated using PPR vaccine. Sheep in groups D and E were then infected with 5 x 105 trypanosomes per ml of Tc one (1) week post vaccination (PV) while sheep in groups C and D were treated at 3 weeks post infection with diminazene aceturate. A prepatent period of 12-14 days was observed and antibody titres detectable at one (1) week PV in all vaccinated sheep. The antibody levels progressively increased to a peak Geometric mean titre (GMT) values of 181.0, 222.9, 78.8 and 4.0 for groups B, C, D and E respectively at 8 week PV. Parasitaemia was followed by a depressed sero-conversion rate of antibody. Treatment however enabled the vaccinated Tc infected sheep to mount antibody responses that was superior to that of the infected untreated group. The effectiveness of PPR control programme in trypanosomosis endemic areas could be undermined by trypanosome-induced immunosuppression. Even so, this could be ameliorated by effective trypanocide chemotherapy.