The　in-plane　optical　anisotropy　(IPOA)　of　c-plane　InGaN/GaN　quantum　disks　(Qdisks)　in　nanowires　grown　on　MoS2/Mo　and　Ti/Mo　substrates　is　investigated　using　reflectance　difference　spectroscopy　(RDS)　at　room　temperature.　A　large　IPOA　related　to　defect　or　impurity　states　is　observed.　The　IPOA　of　samples　grown　on　MoS2/Mo　is　approximately　one　order　of　magnitude　larger　than　that　of　samples　grown　on　Ti/Mo　substrates.　Numerical　calculations　based　on　the　envelope　function　approximation　have　been　performed　to　analyze　the　origin　of　the　IPOA.　It　is　found　that　the　IPOA　primarily　results　from　the　segregation　of　indium　atoms　in　the　InGaN/GaN　Qdisks.　This　work　highlights　the　significant　influence　of　substrate　materials　on　the　IPOA　of　semiconductor　heterostructures.