UPDATE 1-Amerisafe 4th-qtr oper profit lags Street

* Q4 oper EPS $0.32 vs est $0.35

* Q4 EPS $0.45 vs $0.46 a year ago

* Q4 expenses up 30 pct at $65.4 mln

March 1 (Reuters) - Workers' compensation insurer Amerisafe Inc posted a lower-than-expected quarterly operating income, hurt by a sharp rise in costs.

The company's fourth-quarter net income fell to $8.1 million, or 45 cents a share, from $8.5 million, or 46 cents a share, a year ago.

On an operating basis, the company -- which caters mainly to businesses in hazardous industries, including construction, logging and trucking -- earned 32 cents per share.

Analysts on average had expected the company to earn 35 cents a share, according to Thomson Reuters I/B/E/S.

Net investment income rose 4 percent to $6.8 million, while net premiums earned rose 17 percent to $66.2 million.

Expenses rose almost 30 percent to $65.4 million.

Net combined ratio rose to 98.4 percent at Dec. 31 from 89.2 percent a year earlier. Combined ratio is the percentage of premiums an insurer has to pay out in claims and expenses, and a lower number means the insurer makes more money.

The DeRidder, Louisiana-based company's shares, which touched a year-low of $15.58 last August, have since gained about 44 percent. They closed at $22.39 on Thursday on the Nasdaq. (Reporting by Aman Shah in Bangalore; Editing by Don Sebastian)