- A&D Co
- A&T Corp
- A.L.M.T. Corp
- ABILIT Corp
- Acces Co
- Access Co
- Ace Koeki
- Acom Co
- Aderans
- ADM Inc.
- Adtec Plasma Technology
- Advanced Technology & Systems Co
- Advanex
- Advantest
- Aeon Co
- Agasta
- Agrex Inc
- Aichi Steel Corporation
- Aida Engineering
- Aim Services
- Aioi Insurance
- Aiphone
- Air Liquide Japan (Teisan)
- Airex
- Airtech Japan
- Aisan Industry
- Aisin Seiki
- Aiwa
- Ajinomoto
- Akai Electric
- Akebono Brake Industry
- Akita Bank
- Alinco
- All Nippon Airways
- Almedio Inc
- Aloka
- Alpha Corporation
- Alpha Systems Inc
- Alpine Electronics
- Amada Co
- Amada Sonoike
- Amano Corporation
- Ando Electric
- Anest Iwata Corporation
- AnGes MG
- Anritsu Corporation
- AOC Holdings (former Arabian Oil Co.)
- AOI Advertising Promotion
- Aoi Electronics
- Aomori Bank
- Aoyama Trading
- APIC Yamada
- Aplix Corporation
- Applied Technology
- Arakawa Chemical Industries
- Area Quest Inc
- Ariake Japan
- Arisawa Mfg
- Artist House
- Artiza Networks
- As One Corporation
- Asahi Bank (now Resona Holdings,Inc)
- Asahi Breweries
- Asahi Broadcasting
- Asahi Denka Kogyo
- Asahi Glass
- Asahi Intecc
- Asahi Kasei Corporation (formerly Asahi Chemical Industry)
- Asahi Optical (now Pentax Corp)
- Asahi-Seiki Manufacturing
- Asashi Pretec Corp
- Asatsu-DK Inc
- Ascii
- Asia Securities Printing
- Asics Corporation
- ASKUL Corporation
- ASO FOAM CRETE
- Asset Managers Co
- Ataka Construction &Engineering
- Atlus
- Atol
- Atomix Co
- Atsugi Co
- Aucnet Inc
- Axell Corp
- Aplix.co.jp/en/index.html