A few importers of marine products has practiced ice glazing of frozen fish and forced water injection into small octopus to increase their weight. These rampant practices have recently become a serious social issue. Therefore, this study was conducted to develop non-destructive detection methods for verifying forced water injected frozen small octopus using dielectric properties. The weight and dielectric properties of live small octopuses imported from China were measured using an electronic scale and dielectric probe connected with vector network analyzer, respectively. The frequency range from 0.5 to 4 GHz was used for measurement of dielectric properties of small octopus samples. The moisture contents of live small octopuses were determined by convection drying at 105°C for 24 h. To increase weight of small octopus samples, each sample was placed in a container including 2% polyphosphate solution of 800 mL and was kept for 24 h in a refrigerator. Then, the sample was removed from the solution and was frozen at -35°C for 24 h. The moisture contents of live small octopuses were 81.6 ± 1.9% (wb). Regardless of weight of live small octopuses, dielectric constant (ε′) and dielectric loss factor (ε′′) were from 76.09 to 58.62 and from 101.95 to 28.72, respectively. The average weight gain of small octopuses immersed in the solution was approximately 40.6%. Dielectric constant (ε′) and dielectric loss factor (ε′′) of forced water injected small were from 78.18 to 66.71 and from 51.96 to 25.05, respectively. In addition, there was a significant difference between dielectric properties and penetration depth of fresh frozen and forced water injected frozen small octopuses. The results clearly showed that dielectric properties of small octopuses affected by moisture contents could be an important factor to detect forced water injected frozen small octopuses.