A pneumatic radial tire comprising a carcass layer (4a, 4b) mounted between a pair of beads, a belt layer (6a, 6b) on an outer peripheral side of the carcass layer (4a, 4b) in a tread portion, and a belt reinforcing layer and a tread rubber on an outer peripheral side of the belt layer (6a, 6b); the belt reinforcing layer comprising a double-twisted composite fiber cord having one aromatic polyamide fiber cord and one aliphatic polyamide fiber cord twisted therein; characterized in that a total fineness of the composite fiber cord ranges from 1800 to 3200 dtex; an elongation under a load of 2.0 cN/dtex ranges from 3.0 to 4.0%; a rubber composition constituting the tread rubber is formed by compounding from 10 to 110 parts by weight of a silica having a nitrogen adsorption specific surface area of not less than 100 m 2 /g with 100 parts by weight of a diene rubber; - the rubber composition constituting the tread rubber further contains from 50 to 90 wt.% of a terminal-modified solution polymerized styrene butadiene rubber having a styrene unit content of from 30 to 45 wt.% and a vinyl unit content of from 30 to 50 wt.% in 100 wt.% of the diene rubber; - the tensile stress at the time of 100% deformation of the rubber composition at 100°C is not less than 2.0 MPa; and a loss compliance of the rubber composition at 60°C is not more than 45 Pa -1, wherein the loss compliance L is determined by the following general formula; LC = E " / E * 2 wherein LC is the loss compliance in Pa -1, E" is the loss modulus in Pa, and E ∗ is the complex modulus of elasticity in Pa, wherein the complex modulus of elasticity E ∗ and the loss modulus E" of the rubber composition are measured in accordance with the provisions set forth in JIS K6394 using a viscoelastic spectrometer under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and a temperature of 60°C and wherein the tensile stress at the time of 100% deformation at 100°C is measured in accordance with JIS K6251 by performing a tensile test at 100°C using a No. 3 dumbbell-shaped test piece and measuring the tensile stress at the time of 100% deformation. the belt reinforcing layer comprising a double-twisted composite fiber cord having one aromatic polyamide fiber cord and one aliphatic polyamide fiber cord twisted therein; characterized in that a total fineness of the composite fiber cord ranges from 1800 to 3200 dtex; an elongation under a load of 2.0 cN/dtex ranges from 3.0 to 4.0%; a rubber composition constituting the tread rubber is formed by compounding from 10 to 110 parts by weight of a silica having a nitrogen adsorption specific surface area of not less than 100 m 2 /g with 100 parts by weight of a diene rubber; - the rubber composition constituting the tread rubber further contains from 50 to 90 wt.% of a terminal-modified solution polymerized styrene butadiene rubber having a styrene unit content of from 30 to 45 wt.% and a vinyl unit content of from 30 to 50 wt.% in 100 wt.% of the diene rubber; - the tensile stress at the time of 100% deformation of the rubber composition at 100°C is not less than 2.0 MPa; and - the rubber composition constituting the tread rubber further contains from 50 to 90 wt.% of a terminal-modified solution polymerized styrene butadiene rubber having a styrene unit content of from 30 to 45 wt.% and a vinyl unit content of from 30 to 50 wt.% in 100 wt.% of the diene rubber; - the tensile stress at the time of 100% deformation of the rubber composition at 100°C is not less than 2.0 MPa; and a loss compliance of the rubber composition at 60°C is not more than 45 Pa -1, wherein the loss compliance L is determined by the following general formula; LC = E " / E * 2 wherein LC is the loss compliance in Pa -1, E" is the loss modulus in Pa, and E ∗ is the complex modulus of elasticity in Pa, wherein the complex modulus of elasticity E ∗ and the loss modulus E" of the rubber composition are measured in accordance with the provisions set forth in JIS K6394 using a viscoelastic spectrometer under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and a temperature of 60°C and wherein the tensile stress at the time of 100% deformation at 100°C is measured in accordance with JIS K6251 by performing a tensile test at 100°C using a No. 3 dumbbell-shaped test piece and measuring the tensile stress at the time of 100% deformation.