|Hiroshi's uncle||Hiroshi's aunt|
 Kurisuke Agasa
Kurisuke was the professor's uncle. He was sick during his whole life and died at age 38. He lived in a big house with his sister Teiko, who was the only person he trusted. At one point he hired a painter to paint a portrait of them. After his death he wished in his will that his house would be standing as he left it for 50 years.
 Teiko Agasa
Teiko was the aunt of the professor. She worked a school teacher and lived with her brother in his house. At one point she became acquainted with a painter who made a portrait of the siblings. After her brother's death she moved out. Around 15-16 years prior to the series, she began receiving coded letters once a year for ten years. They were written in hiragara but was decorated with a code. Since she didn't understand them, she ask the professor for help, who ask Yusaku. Yusaku broke the code and gave the professor the answer to pass on to his aunt, but it's unknown what she did afterwards. The letters were from the painter, who was hiding from a man, that had hired him to create a bill plate for counterfeiting. The painter was hiding in Kurisuke's house and wrote the letters to let Teiko know of this and entrust her the plate, but she never got the plate, since Conan found it on the dead man's person. Later on Teiko died a year prior to the series at age 76, unmarried.
- Agasa mentioned having a cousin, who has a granddaughter.