In many coastal environments the bulk of the particulate material is aggregated. There is, however, to date, no treatment of how aggregation affects the optical properties of oceanic particulate material. Such treatment is needed to constrain suspended particulate material inferred from measurements using optical sensors. Here, using in-situ manipulations of natural particulate populations, we present observations showcasing directly some effects of aggregation on the optical properties of the bulk particulate material. We introduce a model, based on the work of Latimer, to assess aggregation effects on optical properties and show the possible biases associate with incorrectly modeling aggregates as solid particles. The model is constructed from the average optical properties of a coated sphere model and a homogeneous spheroid model, and has been found to work well when compared to laboratory results of aggregation of polymer beads. In addition, we find that aggregation can provide a simpler explanation for the canonical relationship observed between suspended mass and particulate attenuation or scattering (e.g. Babin et al., L&O 2003).Boss, E., W.H. Slade, P. Hill, K. Curran, T. Milligan, and B. Law, 2008. Optical Properties of Oceanic Aggregates; Field Examples and a Modeling Study. 2008 Ocean Sciences Meeting, Orlando, FL, March 2-7.