Khmelnytskyi Oblast (Ukrainian: Хмельницька область, romanized: Khmelnytska oblast), also known as Khmelnychchyna (Ukrainian: Хмельниччина), is an oblast (province) in western Ukraine covering portions of the historical regions of western Podolia and southern Volhynia. The administrative center of the oblast is the city of Khmelnytskyi. The current estimated population is around 1,228,829 (2022 estimate).

Created in 1937 out of border okrugs of Vinnytsia Oblast, in 1941–44 it was under Nazi Germany occupation and part of the Reichskommissariat Ukraine (Wolhynien und Podolien general district). Following the Kamenets-Podolsky pocket in spring of 1944 as part of the Proskurov-Chernovtsy operation, Soviet troops removed the German occupation in the region. Until 4 February 1954 it was called Kamianets-Podilskyi Oblast (Ukrainian: Кам'янець-Подільська область, romanized: Kamianets-Podilska oblast) and was centered in Kamianets-Podilsky until 1941. The region rebranding took place after the official renaming of the region's administrative center to Khmelnytskyi.

Khmelnytskyi Oblast has a total area of 20,600 km² (7,953.70 sq mi) (3.4% of the total area of Ukraine) and is located between 48°27' and 50°37' north latitude and between 26°09' and 27°56' east longitude. It is 220 km (136.70 mi) long when measured from north to south, and is 120 km (74.56 mi) in length when measured from east to west. It is associated with a historical region of Podolia, yet in reality its territory is split almost in half, the northern in Volhynia, and the southern in Podolia. Its Volhynian region contains smaller cities like Iziaslav, Starokostiantyniv, Shepetivka, while its Podolian portion more developed cities of Khmelnytskyi and Kamianets-Podilskyi.

The oblast borders the Rivne Oblast to the northwest, the Zhytomyr Oblast to the northeast, the Vinnytsia Oblast to the east, the Chernivtsi Oblast to the south, and the Ternopil Oblast to the west.

The Podolian Upland (270–370 meters above sea-level) occupies the central area of the Khmelnytskyi Oblast. The northwestern areas of the oblast are part of the Volyn highland (highest point — 329 m above sea-level), while to the north, the oblast claims a part of the historic region of Polissia (highest point — 200–250 m above sea-level). The southwestern territory of the Khmelnytskyi Oblast is crossed by the Tovtry range (Ukrainian: Товтровий кряж, romanized: Tovtrovyi kriazh), which includes Mount Velyka Buhaikha (Ukrainian: Велика Бугаїха), the highest point of the oblast at 409 m above sea-level. The extreme south of the oblast has a surface with canyon-like river valleys. The Dniester Reservoir located there is the lowest point of the oblast (121 m above sea level).

There are 120 rivers with a length of 10 km (6.21 mi) or more in the Khmelnytskyi Oblast. The largest of these are the Dniester River (which flows for 160 km (99.42 mi) within the oblast), as well as its tributaries: Smotrych, Ushytsia, and the Zbruch — and the Southern Buh River (which flows for 120 km (74.56 mi) within the oblast), as well as its tributaries: Buzhok, Ikva, and Vovk. The rivers of the Dnieper River's basin — Horyn, Khmora, and Sluch Rivers also run through the oblast. The oblast's lakes are located mostly in basin of the Horyn River. The largest reservoir in the oblast is the Dniester Reservoir.

There are 1858 ponds and/or reservoirs in the oblast. The largest of these include Shchedrivske (with a surface area of 12.58 km² (4.86 sq mi)), Novostavske (with a surface area of 11.68 km² (4.51 sq mi)), and Kuzmynske (with a surface area of 7.65 km² (2.95 sq mi)).

Historic administrative affiliation of the area: