The Iyo dialect (伊予弁, Iyo-ben) of Japanese is spoken by people from Ehime Prefecture in Japan. The name is a remnant of the Ehime area's historical name, Iyo Province.

Accents vary somewhat by geography within the prefecture. The southern area is particularly influenced by the Kyūshū dialect, while the central and eastern districts have accents similar to Kansai dialect.

The Iyo dialect has numerous characteristics that differentiate it from standard Japanese grammar.

• ya (や) replaces da (だ) as the casual copula
• ken (けん) replaces kara (から) as in "because"

• yaken (やけん) is used instead of dakara (だから)

• oru (おる) replaces iru (いる) as the verb "to be" for animate objects

This leads to two alternate conjugations of the continuative form (～ている -te iru):

• -toru (～とる) is a contraction of -te oru
• V-stem + -yoru (～よる) is a slurring of oru

Example: "What are you doing?" (何してるの？ nani shiteru no? in standard Japanese) becomes either

• nani shitoru no? (何しとるの？) or
• nani shiyoru no? (何しよるの？)

• n (ん) as a contraction of sentence-final no (の)

Example: The second "What are you doing?" above, nani shiyoru no? is often contracted to nani shiyon? (何しよん？) or nani shon? (何しょん？)

• ya and wai (わい) can be emphatic sentence-final particles, like yo (よ)
• Negative potential forms ("can't X") are sometimes expressed as yō + V-neg. (yō is an onbin of 良く yoku, so literally, "not well Xed")

Example: "Can't do" (できない dekinai in standard Japanese) becomes yō sen (ようせん）

"Can't go" (行けない ikenai in standard Japanese) becomes yō ikan （よう行かん)

• Especially among the elderly, kogai (こがい), sogai (そがい), and dogai (どがい) are used for "this (kind of~)", "that (kind of~)", and "which (kind of~)", respectively (konna こんな, sonna そんな, donna　どんな in standard Japanese).
• zonamoshi (ぞなもし) is the most famous sentence-final particle of Iyo dialect due to being used in Botchan, a famous novel by Natsume Sōseki, but the usage is now obsolete.

Some of the vocabulary in the dialect is readily understandable by speakers of standard Japanese, but many items are so different as to cause significant confusion. An example often proffered by locals is kaku かく, "to move/carry". For instance, it might be used in the context of a classroom—"Move your desk" (机をかいて tsukue o kaite). This would be incomprehensible to a non-local; a speaker of standard Japanese would interpret this as either "draw a desk" or "scratch your desk".