To provide a pneumatic bias tire for a heavy load, improved in high- speed durability and load durability while reducing the weight thereof.

This pneumatic bias tire for a heavy load uses a polyolefin ketone fiber cord expressed by the formula, -(-CH2-CH2-CO)n-(R-CO)m- for a carcass layer. In the formula, 1.00≤(n+m)/n≤1.05, and R means an alkylene group having three carbon or more. The polyolefin ketone fiber cord has the high strength, and a sufficient strength of a carcass layer can be obtained by using the polyolefin ketone fiber cord for the carcass layer even in the case of reducing the diameter to reduce the weight thereof. Despite the high strength, the cord has excellent adhesiveness to rubber and the excellent bending fatigue resistance, and thereby a tire having excellent load durability can be obtained.