The power of dynamic marketing capabilities (DMC) to explain business portfolio expansion of agribusiness- based SMEs in Rivers State was assessed in this study. The study looked at DMC in terms of market-sensing, opportunity-seizing, customer-bonding and channel-linking capabilities, while business portfolio expansion was treated unidimensionally. An explanatory research design was adopted. Data for the study was collected via cross-sectional survey, using structured questionnaire. Validity and reliability of the questionnaire was ascertained using exploratory factor analysis and Cronbach’s Alpha test respectively. 90 SMEs in agribusiness were surveyed. However, after data cleaning, data collected from 77 respondents was used in the final analyses. Multiple regression analysis was the test statistic used, and was facilitated by the Statistical Package for Social Science (SPSS) version 24.0. The results indicate that DMC have strong positive influence on business portfolio expansion of agribusiness-based SMEs in Rivers State; and that ability to seize opportunity has the strongest influence on BPE among the studied population. The study concludes that DMC (opportunity-seizing, customer-bonding, channel-linking and market-sensing capabilities) inform business portfolio expansion of agribusiness-based SMEs in Rivers State; and recommends that agro-based SMEs in Rivers State that seek business portfolio expansion should acquire or develop and deploy opportunity-seizing, customer-bonding, channel-linking and market-sensing capabilities to enhance their ability to identify, assess and invest in viable business opportunities; as well as build close-knit relationship with customers and alliances with channel members.