BACKGROUND: The effect of Human Immunodeficiency Virus-1 (HIV-1) on CD4+ Th2 cells is hypothesized to affect parasitological diagnosis of Schistosoma mansoni using Kato Katz technique. Thus, the use of more sensitive technique such as Point-of-Care Circulating Cathodic Antigen (POC-CCA) test is recommended. However, the sensitivity of this diagnostic test in diagnosing S.mansoni infection and the usefulness of it in monitoring efficacy of praziquantel drug in presence of HIV-1 co-infection remains inconclusive. The Primary objective of the present study was to assess accuracy of the POC-CCA test in diagnosing S.mansoni infection before and after praziquantel treatment in adult population co-infected with HIV -1. METHODS: A prospective longitudinal study was conducted among individuals aged 15-55 years at Igalagala village, north-western Tanzania. At baseline and 4 weeks after treatment, a single stool and urine samples were collected from each participants. Kato Katz (KK) technique and Point-of-Care Circulating Cathodic Antigen tests were used for diagnosis of Schistosoma mansoni. RESULTS: At baseline, based on KK and POC-CCA, the prevalence of S.mansoni was 57.8% (95%CI: 52.9-62.4) and 87.5% (95%CI: 83.9-90.4). Based on KK technique and POC-CCA test, 3.6% and 5.7% of the study participants were co-infected with S.mansoni and HIV-1. At baseline, in the general population, the sensitivities of POC-CCA test using KK technique and combine gold standard were 96.3%(95%CI: 93.1-98.3) and 97.6%(95%CI:95.5-98.9) respectively. In the HIV-1 seropositive group, at baseline, the sensitivities of POC-CCA test using KK technique and combined gold standards, were 93.3%(95%CI:68.1-99.8) and 96%(95CI%:79.6-99.9). Four weeks after treatment, in general population, the sensitivities of POC-CCA test using KK technique and combined gold standards were 47.8%(95%CI:26.8-69.4) and 84.4%(95%CI:74.4-91.7). In the HIV-1 seropositive group, using KK technique, the sensitivity was 100% (95%CI:2.5-100). CONCLUSION: The sensitivity of POC-CCA in diagnosing S.mansoni infection was higher than KK technique in adult individuals likely to have low infection intensity and co-infected with HIV-1. However, its sensitivity decreases following praziquantel treatment but remained higher than Kato Katz technique. If the goal of the post-treatment is to identify uncured individuals, then POC-CCA test offers the best choice.