Mangrove or Mangal vegetation are typical wetland ecosystems found in coastal deposits of mud and silt throughout the tropics and some distance into the sub-tropical latitude. Species diversity, distribution, seasonal abundance in population and behavioral responses of mangrove associated molluscs (gastropods and bivalves) were investigated in two mangal areas: Sandspit and Korangi, along the Karachi coast of Pakistan. For sampling, a fixed route was followed throughout the study period and the samples were collected and observations were made from HTZ to LTZ. Fourteen species of molluscs (5 Prosobranchia; 6 Pulmonata; 1 Opisthobranchia and 2 Lamellibranchia) belonging to ten families were recorded. Family Ellobiidae, Potamididae, and Onchididae were found extensively distributed in both sites. All the recorded species are belonging to the epifaunal mode of life. Analysis of the data shows that ten of the recorded species are common to both sites, while four are exclusively found at the Korangi site. Seven of the representative species are exclusively mangrove associated; five are common to mangrove and non-mangrove areas, while two are non-mangrove dwellers. The low species diversity can be attributed either to the study techniques, a small number of study sites or possibly to the geographical locations of the study sites. Seasonal variations were noticed in species diversity and density distribution, indicating higher values in summer and autumn and lower in spring and winter.