Additive manufacturing (AM) offers the opportunity to enhance the mechanical performance of metallic honeycomb structures. However, there is limited research on the load-rate effects affecting in-plane compression. For the first time, this study investigates the in-plane compressive performance of Steel 316L honeycomb structures produced via material extrusion (ME) and laser powder bed fusion (LPBF). ME honeycombs of three cell sizes and single-cell size LPBF honeycombs were tested under uniaxial compression at varying quasi-static loading rates. Digital image correlation (DIC) was also employed to capture the deformation modes of the honeycombs and to map the local strain fields during compression. Empirical models were used to predict the in-plane compressive performance of the honeycomb structures. Particularly for the plastic collapse stress, an empirical formula incorporating viscoplastic dependency on the cell wall material within the quasi-static loading regime has been derived, producing accurate predictions. Both types of honeycomb structures are load-rate sensitive, as their compressive mechanical properties improved with the load rate increase. Moreover, the variation of the cell size was found to optimise the in-plane compressive performance. The deformation mode for both honeycomb structures was confirmed to be cell wall bending, plastic buckling, cell wall collapse, and folding.