Perairan Morodemak merupakan daerah muara yang diduga mengalami perubahan kondisi ekologi perairan disebabkan karena pengaruh sedimentasi dan masukkan bahan organik yang berasal dari akumulasi aktivitas masyarakat. Makrobentos merupakan salah satu hewan yang dapat dijadikan indikator. Hewan ini sangat peka terhadap perubahan kualitas air tempat hidupnya sehingga akan berpengaruh terhadap komposisi dan distribusinya. Penelitian ini dilaksanakan dengan tujuan mengetahui tekstur vertikal sedimen dan kandungan bahan organik serta keanekaragaman makrobentos di Muara Sungai Tuntang, Morodemak. Metode penelitian yang digunakan dalam penelitian ini bersifat deskriptif, pengambilan sampel dilakukan di 8 titik sampling di sekitar muara. Pengambilan sampel meliputi sedimen dasar perairan dan makrobentos, kemudian dilakukan analisa di laboratorium. Hasil penelitian dari 8 titik sampling di Muara Sungai Tuntang, Modrodemak struktur sedimen mempunyai kriteria lumpur dan liat. Kandungan bahan organik pada lapÃsan atas berkisar antara 5,36 – 8,16%, lapisan tengah berkisar antara 4,7 – 9,06%, dan lapisan bawah antara 4,13 – 8,58%. Keanekaragaman makrobentos dari 8 titik sampling ditemukan sebanyak 10 spesies dari 3 kelas yang termasuk dalam 2 filum yaitu moluska (5 spesies) dan polychaeta (5 spesies). Nilai kelimpahan makrobentos pada seluruh pengambilan sampel berkisar antara 0 – 1232 idividu/m2. Indeks keanekaragaman berkisar antara 0 – 1,33. Indeks keseragaman 0 – 1. Parameter kualitas perairan menunjukkan variasi dan dinamika yang masih dalam toleran dan mendukung kehidupan makrobentos. Morodemak waters is an estuary area which is suspected of changing ecological water conditions due to the influence of sedimentation and organic matter that enter from the accumulation of society activities. Makrobentos is one of the animals that can be used as an indicator. These organisms are very sensitive to changes of water quality where they live that will affect their composition and distribution. This research was conducted with the purpose of knowing the vertical structure of sediment and organic matter content as well as diversity of makrobentos in the estuary of Tuntang, Morodemak. The methods of this research is descriptive, sampling was performed in 8 sampling points around the estuary. Sampling includes the bottom sediment and makrobentos, then analyzed in the laboratory. The results of the 8 sampling points in Tuntang estuary Modrodemak, sedimentary structures has mud and clay criteria. The content of organic matter in the upper layer ranges between 5,36 to 8,16%, the middle layer ranges from 4,7 to 9,06%, and the bottom layer between 4,13 to 8,58%. Diversity of makrobentos of 8 sampling points are found as many as 10 species of 3 classes included in the phylum mollusk 2 (5 species) and Polychaeta (5 species). The abundance values of Makrobentos across all samples ranged from 0 – 1232 ind/m2. Diversity index ranged from 0 – 1,33. Uniformity index of 0 - 1. Water quality parameters showed variations and dynamics which are still in a tolerant and support makrobentos life.