The prevalence of on-street parking in the city of Aba has continued to generate much concern to all road users and the government in Nigeria as it hinders traffic flow and increases traffic accidents. Consequently, the government initiated the policy of on-street parking prohibition at the downtown area of Aba, leading to increased travel difficulty for motorists. This study examined the policy of on-street parking prohibition and the resultant travel behaviour of motorists. The study adopted survey design whereby primary data were collected with the aid of structured questionnaire, measurement, and observation. The sample size of 400 respondents was determined from the study population of 420,665 motorists using the Standard Traffic Count (STC) approach. Cluster, purposive and simple random sampling techniques were used to proportionately select the roads and respondents used in the study. Analysis of variance (ANOVA) and Chi-square were used for data analysis. The study revealed among other thing that: there were significant differences in the geometric characteristics of roads where on-street parking was prohibited and where on-street parking was not prohibited. On-street parking prohibition was found to have impacted the travel behaviour of motorists as follows: (i) motorists travel less with single occupancy vehicles (SOVs) but more with KEKE (tricycle) during the working hours; (ii) there is reduction in the frequency of trips by motorists to the city centre whereas they divert to the outlying areas; and (iii) there is increased city bound (non-work) trips during early morning and late evening hours. It was recommended among others that government should embark on the construction of modern off-street parking facilities at designated locations within the city of Aba. Government should also recover sidewalks and road setbacks which have been totally invaded by commercial activities in Aba, and develop paid curb-parking there as alternative to on-street parking.