Sweetpotato (Ipomoea batatas L.) has a diverse range of positive characteristics including high yield per unit area, nutritional value, and resistance to several production stresses. However, diagnostics aspects for detection of sweetpotato feathery mottle virus (SPFMV) are not well understood. This paper documents such aspect via expression of SPFMV coat protein. A pGEX glutathions S-transferase (GST) fusion protein system was used to express the coat protein of the sweet potato feathery mottle virus in E. coli. The fusion protein was affinity purified from the crude extract of total bacterial protein in a soluble native form and used as an antigen for mice immunization without the need to cleave the GST carrier. The resultant antiserum was implemented for viral diagnostic purposes using dot-ELISA technique as a reliable qualitative method. Raised antiserum was efficient to detect the viral infection in sweetpotato plants when dilution of up to 1/15,000 was used for detection. The recommended antiserum dilution ranged from 1/8000 to 1/10,000 in which no background from the antiserum in either the healthy samples or the filters was observed.