National Highway 31 (NH 31) is a primary National highway of India. It starts from Gadan Khera in Unnao at Uttar Pradesh, passes through Bihar, and terminates at its crossing with State Highway 10 (West Bengal) at Kodubari Morh in Gazole at Malda district of West Bengal. The road continues as SH 10 (WB), which connects Gazole to Hili near Bangladesh Border (Hili Railway Station).

National highway 31 transits 1,047 kilometres (651 mi) across three states of India in east - west direction.

Unnao, Lalganj, Raebareli, Salon, Pratapgarh, Machhlishahr, Jaunpur, Babatpur, Varanasi, Ghazipur, Ballia, Suraimanpur

Chhapra, Hajipur, Patna, Bakhtiyarpur, Barh, Mokama, Barauni, Begusarai, Khagaria, Bihpur , Naugachia, Kursela, Korha, Katihar, Bastaul, Pranpur, ,Purnia,

Chandpur, Harishchandrapur, Tulsihata, Chanchal, Malatipur, Samsi, Akalpur, Kodubari Morh at Gazole.

As per Satellite imagery from Google Maps, the national Highway 31 is being made 4 lane currently between Unnao & Raebareli, between Ghazipur & Ballia, between Bakhtiyarpur & Barauni, between Katihar & Labha. 4 lane Bypass is under construction between Labha & Harishchandrapur for bypassing Chandpur (West Bengal). 4 Lane bypass is under construction at Chanchal to bypass Chanchal Town bottleneck. Once these bypasses are built, the Highway length will shorten to 992.25 kilometres (616.56 mi) & reducing travel time. 4 lane stretch is already operational in patches between Raebareli & Ghazipur, between Hajipur & Bakhtiyarpur & between Katihar & Barauni.