The Chubb Corporation reported $506 million in net income for the 2012 first quarter, down slightly — 0.59% — from $509 million income reported one year ago.

The insurer’s underwriting profit improved significantly, but it was offset by weaker realized investment gains.

Net written premiums for the first quarter were $2.947 billion, up 3 percent from $2.859 billion one year ago.

Underwriting income for the quarter was $303 million, up 50 percent from $202 million one year ago.

The combined ratio for the quarter was 90.2 percent, improving from 93.7 percent during the prior-year period. Catastrophe losses had a much smaller impact in the latest quarter. The CAT losses for the first quarter represented 0.8 percent. One year ago, however, CAT losses represented 9.5 percent of the combined ratio.

Investment income was $380, down slightly from $381 million from the year-ago period. But realized investment gains after income tax fell to $37 million, down 64 percent from $104 million one year ago, related mostly to the company’s “alternative investments.”

U.S. Average Commercial Insurance Renewal Rates Up 8%

Like its competitor Travelers, Chubb also said its business insurance renewal prices are continuing their upward movement. Chubb’s U.S. average commercial insurance renewal rates were up 8 percent in the 2012 first quarter, with renewal premium retention of 83 percent. And the ratio of new-to-lost business was 0.9 to 1.

“Chubb is off to a strong start in 2012,” said CEO John Finnegan. “We produced excellent results in the first quarter, with operating income per share of $1.70 and a combined ratio of 90.2 percent.”

“We are especially encouraged by the momentum of renewal rate increases we experienced during the quarter in both standard commercial and specialty lines, as well as the continued rate improvement in personal lines.”

Below are more detailed figures from three main business segments.

Personal Insurance Segment

In this segment which include auto, homeowners and other, net premiums written were $940 million, up 5 percent from $894 million one year ago. The combined ratio was 85.5 percent, improving from 93.8 percent. Catastrophes losses accounted for 1.2 percentage points in this segment’s combined ratio, down from 7.8 points one year ago.

Commercial Insurance Segment

In this segment including multiple peril, casualty, workers’ comp, and property and marine, net premiums written were $1.405 billion, up 6 percent from $1.326 billion one year ago. The combined ratio was 93.3 percent, improving from 100.7 percent.

Specialty Insurance Segment

In this segment which offers professional liability and surety, net premiums written were $2.947 billion, up from $2.859 billion during the prior-year period. The combined ratio was 90.6 percent, improving from 93.9 percent.